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Mersenne Primes
Title: Mersenne Primes
Fandom: Numb3rs
Pairing: Don/Charlie
Rating: Mature for adult sexual content, language, mathematics
Length: ~2,300 words
Summary: The first rule of fucking your brother in the shower is -- you do not talk about fucking your brother in the shower. Apologies to Chuck Palahniuk, Fight Club.
Warnings: incest, underage (NOT statutory), angst, elementary number theory, POV and verb tense hopscotch
Notes: Deepest thanks go to jaredsexual for holding my hand and goblin_dae for cheering me on, no matter how wacky it got. Loving goblin_dae for the final nitpicky beta. Takes place during 2x4, Calculated Risk - it's not hard to guess where. No spoilers, though.

Mersenne Primes

FACT: For every non-negative integer where 2n-1 is prime, (2n-1)2n-1 is perfect.

Don is n. Don has always been n, in Charlie's mind; so long as Don is a known quantity, everything else falls into place. Charlie is a function of Don.

For all the times he and Don have been out of touch with each other (Princeton, Albuquerque, periods of varying length during grade school, …), Charlie's life can be expressed as 2n-1. In these cases, Charlie is decreased by a fundamental unit – one that he hasn't been able to name, as of yet, but that he has unarguably observed.

Every time Don spends the night at the house, it's because he is in a 2n-1 situation. It's because Don's term is subtly yet undeniably lacking in that same fundamental unit, and it's because Don, being Don, internalizes it.

Charlie's been standing outside the bathroom door for over a minute, now, listening to the shower run and knowing it's not their father for two distinct reasons: one, Alan sings in the shower (under his breath and mildly off-key, but still), and two, it's early enough in the morning that he should still be asleep. Also, thirdly, the water vapor slithering out from under the door carries the scent of Don's shower gel, sharp and brisk.

Charlie takes a deep breath, holds it for a count of twelve, and then he leans on the doorknob to keep it from clicking and to keep the hinges from creaking as he slips inside.

"Charlie? That you?" Don's voice is loud enough to be heard above the shower from a foot and a half away – no louder – and between that and the fact that Charlie's barely taken his hand off the doorknob, he knows that Don's asking an entirely different question.

Charlie takes another twelve-count breath, but he only makes it to eight before his pajama pants hit the floor and he breathes out, "Yeah."

Don's body never fails to be a source of both shock and fascination for Charlie. Long years of stubborn dedication bordering on the obsessive write themselves in every plane and angle, and each scar tells another story of Don's refusal to think of himself before others.

Charlie looks, and Don lets him; Charlie watches his brother scrub the cloth over his arms, his chest, across the back of his neck. He reaches forward and rests his open palm beneath Don's ribs; Don brushes his thumb down from Charlie's wrist to his elbow, and when his fingers close around Charlie's arm Charlie shuffles forward and bumps his cheek against Don's chest. He keeps it there, because he's actually still kind of waking up. "You didn't sleep in your room last night."

Don shakes his head. "I just came up for a shower," he says, running sudsy fingertips through Charlie's hair.

"Oh. Okay." Charlie picks his head up and yawns a little just before he kisses Don.

From an objective standpoint, the taste combination of shower gel and morning breath is terrible, but Charlie's palate has been conditioned to appreciate it. It's the flavor of every before-the-rest-of-the-house-wakes-up morning encounter, and it launches a relentless sequence of remembered images and sensations. Charlie buries the fingers of both his hands in Don's spiky-wet hair and kisses him harder, his teeth and tongue ascertaining that Don is experiencing a similar assault from his own memory.

It had started in high school, when Charlie was eleven and unsure of his own body and Don, sixteen, had been the one with all the answers. They'd fooled around a few times, jerking off in Don's bedroom, Charlie studying carefully to make sure he got it right. That had creeped Don out a little, at the time, but mostly it had just meant that Charlie didn't notice at all when Don was staring at him.

Maybe if Charlie had noticed, Don would have stopped.

In their junior year, the whole class had gone on a bus trip upstate. Don hadn't wanted to share a hotel room with Charlie, for a whole lot of reasons, but of course Don wasn't the only one. And the weird kid was his little brother, so when it came right down to it, when Don really let himself think about it (which he didn't do very often, of course, or pretty much ever, because thinking too much about him and Charlie got dangerous), he didn't want to leave Charlie alone with anyone else. Ever.

Charlie would have been perfectly happy to stay in his own room, or not go on the trip, if the school board or his parents had accepted either of those ideas, respectively. He had known that Don had better things to do than babysit his over-intelligent, under-streetsmart little brother. He had known Don would rather have been staying with the other boys his age, calling for pizzas under fake names and staying up late trying to watch mangled pay-per-view. Still, he had appreciated the company.

He'd also walked in on Don in the shower.

The frosted glass blurred detail, but it did nothing to mask the geometrically perfect curve in Don's spine, the intensity of the angle his jaw cut relative to his shoulders, the deceptively complex relationship between the rhythm of his breathing and the speed of his hand. Charlie couldn't help it; he reached out and began to map expressions on the fogged-up glass.

He was beginning to run out of room when he heard his name, not shouted at him in reproach or shock, but barely choked out – "God damn it, Charlie."

He froze. Had Don seen him? It didn't seem likely, based on his inflection, but it was possible. "Don?" It was out before Charlie could stop himself. He heard his brother swear and hit the wall. "I'm sorry. I'm – I'll –"

"Charlie, it's not your fault." Don hadn’t stopped his shower, hadn't even turned down the spray. Hadn't looked at Charlie, who meant to be walking out of the bathroom but found his hand on the shower door instead.

"I know." Charlie didn't believe himself as he said it any more than he believed it was a good idea to step into the shower with Don. The edge of the spray saturated his t-shirt, and lukewarm, soapy water slowly wicked up his pajama pants.

"How long were you standing out there?"

"… Kind of a long time." Charlie glanced at the finger-writing, beginning to fog back up but still identifiable. Don followed his line of sight, and Charlie said, "It's not your fault, Don."

Charlie's t-shirt hit the floor with a loud, wet echo, and his brother's body was hot and slippery against his bare chest. "Charlie, we—" He had to stand on tip-toes to reach Don's mouth.

Charlie feels like he's twelve years old again, like they have to get everything done in ten minutes or less, before they get caught, which is sort of still true. But he tries to remind himself that it's also different, like how if they got caught now they wouldn't have an even slightly viable excuse. He pushes his hips against Don's and loops an arm around his brother's neck, clinging. Don puts a hand with water-softened calluses on Charlie's hip, and Charlie shivers closer.

Even then, Charlie'd known what he wanted and how to get it. He'd stood on his tip-toes and reached for Don's mouth, and Don had kissed him. Charlie had still been growing into his body; he was halfway through a growth spurt and all out of proportion. He couldn't even decently fit into his own clothes, but he'd pressed himself into Don's arms until not-fitting didn't matter. "I'm sorry," he'd whispered against Don's chin.

"Shh." Don had lifted Charlie a little and backed him against the shower wall, and Charlie had wrapped his too-long legs around Don's waist, like it was natural. He was always making it so damn hard for Don to remember that it wasn't.

Don had fucked Charlie with his fingers and thrust their cocks together, watching his little brother squirm and moan. I'm sorry. He didn't know who to blame any more, so by default he blamed himself. I'm so sorry, Charlie. But, then, a part of him really wasn't sorry. And a part of him insisted it was Charlie's fault.


Charlie throws his head back, curls spraying water droplets out behind him like cut crystal, and Don presses his lips to the base of Charlie's throat. "God, Charlie," he whispers, in reverence and fear – in awe. Charlie's always been some kind of angel. Now he's fallen to Don's level, where Don can get a hold of him, and Don's selfish and wants to keep him there. He locks his arms around Charlie's back, and Charlie reaches out to brace himself against the green tile wall.

During the summer, when Don was in baseball, Charlie would sneak into the shower with him in the mornings. Not every morning, but most of them, especially on weekdays when Don had practice early. Their parents would still be asleep, and Don and Charlie would do incredibly stupid shit – desperate, messy blow-jobs; slow, inquisitive hand-jobs; crazy sessions of necking and getting wedged between the tub and the wall. It was stupid, but they were hormonal and addicted to each other and they didn't get caught, not once.

Charlie never had trouble believing in love because he understood prime numbers. He knew people were like primes, each one divisible by just one and itself. He had trouble believing in love because every time he tried to apply the properties of primes to himself, the answer he got was invariably wrong.

What Charlie didn't understand was why he always found that he was only divisible by Don.

He'd presented the issue, once, perching on the edge of the toilet seat while his brother finished showering. He'd hoped Don might have some insight – Don might make it OK. (He'd known even then it was a fallacious conjecture.)

Don hadn't said anything except, "We won't have time for this when school starts," which he'd muttered without meeting Charlie's eyes while he stepped out of the shower and slung a towel around his waist.

"I know," Charlie'd answered as he watched Don shave, and he hadn't been surprised when after that Don started locking the bathroom door.

When Don came back to LA, before he got settled in his own apartment, he stayed at home and didn’t lock the door. Charlie mostly stayed out in the garage, working on math he couldn't finish, and showered at 3 in the morning every couple of days.

One of those not-mornings, he was almost too out of it to notice the bathroom door clicking and creaking and clicking open and shut again behind him. He turned around. Don leaned against the door and rubbed a hand over his face, over the stubble that told Charlie he'd last shaved around noon – probably when he got into the office.

"How's mom?" Charlie balled up his t-shirt and threw it somewhere. He reached past the curtain and turned on the spray.

"She's … OK. Better. Things got pretty bad."


Charlie got into the shower and closed the curtain, and Don was still standing there when he got out.


Don looked like he'd been splashing his face with water. His sleeves were pushed up, his shirt was part-unbuttoned, his tie hung over his shoulders, and his eyes were rimmed with red.

"You look like shit, Don."

"I feel like shit."

Charlie closed his eyes, and when he opened them he was looking at the floor. "I – yeah. It's … It's good Mom's doing better. They upped her pain meds?"

Don grabbed him by the shoulders and Charlie could tell he wanted to shake him. There was a whole speech hovering in the tone of his voice, but he didn't say it. "Charlie."

"Don, I'm sorry. This is how I deal."

"You're not dealing."

"Neither are you."

Don opened his hands on Charlie's shoulders, like he was going to push him away, but then he pulled Charlie into a crushing bear hug. If Charlie concentrated on the stubble scraping across his face, he didn't notice that his brother was shaking a little. "We've just got to get through this," Charlie said, putting his hands on Don's back.

Don pulled away with his shoulders and looked at Charlie, eyes searching and so insecure it made Charlie's head spin. "Where's the 'we'?"

It was neither of them that started it; it was some cosmic force; they mashed their lips together and tried to climb into each other's bodies. They fucked each other against the sink, the edge of the countertop leaving perpendicular welts across both of their spines. They didn’t think; they barely felt.

"We're still not dealing," Charlie said as he pulled his shirt over his head, and Don stopped with his hand on the doorknob.

"I know," he said seriously. "We're just getting through it."

The product of 2n-1 and 2n-1 is a perfect integer. Charlie chews on his lips to stay quiet as he and Don push against each other, hot enough under the cooling water. They're only ever this whole when they're together, and Charlie wishes it didn't make him doubt his math every time. But then, as he always tells people, numbers never lie. And it's true, and he and Don need each other in a way that's too profound for it not to be mathematical.

When he rests his head on Don's shoulder and murmurs, "Proof by exhaustion," Don doesn't get it, but he doesn't argue.

My Two Cents:
I started this fic after the very first number theory lecture I attended. My goal was to finish and post by the time the premiere aired, and LOOK! I JUST BARELY MADE IT! *phew* Any and all feedback is wildly craved welcome. Concrit, if you've got it, is accepted and indeed appreciated, but not required. Hooray for learning mathematics via porn!



For more information on Mersenne numbers and Mersenne primes, go here.

Tags: , , , ,
Mood: accomplished accomplished
Chantey: La Oreja de Van Gogh - La Playa

Hailed 13 Times * Run Up The Colors
hermyone6 From: hermyone6 Date: September 23rd, 2006 12:47 am (UTC) (Link)
I like it. The numbers and the rest. How they both seem very "adult" about this thing between them and yet not.
Sorry, maybe it doesn't make sense. But I like it. A lot. Very well written.
meletor_et_al From: meletor_et_al Date: September 23rd, 2006 04:38 am (UTC) (Link)
thank you. I do understand what you mean, I think. it's hard to describe, but yeah. I'm glad you found it in my writing. thank you very much for your feedback :)
(Deleted comment)
meletor_et_al From: meletor_et_al Date: September 23rd, 2006 04:43 am (UTC) (Link)
oh, the boys are so messed up, they are. but yes -- it's the growing up and with each other parts I was trying to highlight, so I'm very very happy that worked. thank you!
From: rubynye Date: September 23rd, 2006 03:05 am (UTC) (Link)
That's a great use of math, of details, and of a shared, intertwined history. And, I'm not sure how you pulled this off, but the POV switches contributed to rather than distracting from the story.

Also? This is hot like fire. *fans self* Wow.

meletor_et_al From: meletor_et_al Date: September 23rd, 2006 04:53 am (UTC) (Link)
thank you very much. the POV switches were a bit of a hassle at first, but then we started working together and it all came out in the wash. I'm super glad to hear it actually did have a good effect, and I wasn't just making that up.

*g* thank you. may as well toss some porn in with the angst, hm?

.:: curtseys ::.
jaredsexual From: jaredsexual Date: September 23rd, 2006 05:19 am (UTC) (Link)

pr0npr0npr0npr0npr0npr0n! YAY. *cough*

the rest of it was uber spectacular, which you know. :D
meletor_et_al From: meletor_et_al Date: September 23rd, 2006 02:53 pm (UTC) (Link)

thank you, love. I'm glad you think so :D
chelletoo From: chelletoo Date: September 24th, 2006 02:40 am (UTC) (Link)
I like the use of numbers. How Charlie realizes he is a part of Don and it doesn't matter that Don doesn't get the numbers.

Also, a nice look at their earlier years.
meletor_et_al From: meletor_et_al Date: September 25th, 2006 03:00 am (UTC) (Link)
thank you very much. I'm glad the numbers worked for you; I was excited to play with them :)
magickaldreamer From: magickaldreamer Date: September 24th, 2006 05:42 am (UTC) (Link)
What Charlie didn't understand was why he always found that he was only divisible by Don.

Such a beautiful line. I simply adore Numb3rs fics that actually use mathematics. It makes it more real to me.

Apart from that, the hotness melted my brain, so that's going to be it for a comment. ;)
meletor_et_al From: meletor_et_al Date: September 25th, 2006 03:05 am (UTC) (Link)
thank you kindly. I agree -- and I find it nearly impossible to get into Charlie's head without expressing things mathematically, so I'm glad to get positive feedback on that.

I'm glad you enjoyed it :D
(Deleted comment)
meletor_et_al From: meletor_et_al Date: October 3rd, 2006 03:09 pm (UTC) (Link)
I'm -- ok, I'm really not sorry, actually, because this is a better response than I could have hoped for, and pretty much right where I want to land readers (because it's right where the damned boys put me while I'm writing, and that's not fair!). thank you. the emotional slug-in-the-gut is, I think, a recurring theme.
yakkorat_fics From: yakkorat_fics Date: February 14th, 2007 08:08 pm (UTC) (Link)
Oooo! Thank ye kindly for the link! Lovely job, darling! I love it!!!

Seriously, it gave me a little bit of insight into Charlie. I love how he relates everything in life to math. The big things, the little things. It all makes sense in his head when the formula produces the correct answer, and he's unsettled when the equation seems to be unsolvable.

Question: is it "unarguable" or is it "inarguable"?

Hailed 13 Times * Run Up The Colors