I see.
Do computer programmers still use octal? I thought hexadecimal was more common.
Um, yeah. Or maybe “I don’t think–” and he disappears before he can finish the sentence.
Yeah, they use it for jokes. Oh, you mean for programming? Yeah, I’m pretty sure you’re right.
Except that you might assume that “y” was supposed to mean f(x) as in y=f(x)=e[sup]x[/sup], in which case d/dy (e[sup]x[/sup]) = d/dy (y) = 1… which still sort of works as a joke. I guess.
What is lim[sub]x->0[/sub](sin x / n)?
6 (Just cancel the n’s)
I have a really bad one: how do you calculate the angles of a polygon?
It depends on how many saxons there are.
Yeah, I made it up in high school…
Here is the corollary to Sinjin’s posting about Heisenberg:
Cop: Do you know how fast you were going?
Heisenberg: Yes. 57.398567235873 miles per hour. But I’ve got no idea where the Hell I am !!
Regarding the descartes joke.
I doesn’t work for me. If A => B, that doesn’t mean that (not A) => (not B)
I guess the joke is bad for the layperson, good for the somewhat geeky, and then bad for the really geeky.
Monk walks up to a hotdog vendor, vendor says “yeah buddy, what’ll ya have”, monk says “make me one with everything”
Who is a pirate’s favourite scientist?
ARR-henius!
The funny thing about this joke is that it’s exactly how I pictured calculus in my mind.
A wavefunction walks into a bar, collapses, and says to the bartender …
What the fuck are you looking at?
Three scientists were sitting on a park bench. One was a Physicist, one was a Biologist, one was a Mathematician. As they idly watched a building across the street from them, they saw 2 people enter the building. A few minutes later they saw 3 people come out.
“Ah,” said the Physicist, “The initial measurement must have been in error.”
The Biologist said “They must be breeding in there.”
The Mathematician said “If exactly one more person enters the building, it will be empty again.”
It’s been done here before, but: what’s green and commutes?
An abelian grape
You have just surpassed my geek-threshhold.
Huh? 
Along the same lines (and even geekier):
Two electrons walk in to a bar. The first electron says “Bartender, I’ll have a martini.” and the second says “Dammit! I wanted a martini.”
Aren’t they all that way, my friend. Aren’t they all.
I’ve always heard this as “What’s purple and commutes?” You must have tyhose damned seedless California grapes.
JustAnotherGeek – Google “Abelian” and “group”. Heck, I’ll bet you can Google “Abelian Grape” and get the answer.
Is that a joke about the Pauli exclusion principle?
Surprisingly enough, the first Google hit for {abelian grape} is a Mathworld page.
http://www.google.com/search?hl=en&q=abelian+grape&btnG=Google+Search
This one ranks right down there below the e^x joke.
Best one I have is: What’s a mathematician’s pick up line?
Hey baby, let me integrate your curves!
I’m afraid I don’t get this one.
Q: How do you know if a mathematician is extroverted?
A: When he talks, he looks at your shoes.
Three statisticians go duck hunting. A duck flies up into the air, and the first statistician takes a shot at him. He misses by five feet to the right. The second statistician aims and fires, but he’s off by five feet to the left.
The third statistician says “Hooray! We got him!”
I heard both of those from Dr. John Allen Paulos.
Descartes is drinking in a bar. Nearing closing time, the bartender asks him if wants another. Descartes says “I think not,” and disappears.