Proof. Assume towards a contradiction that there is an uninteresting positive integer. Then there must be a smallest uninteresting positive integer. But being the smallest uninteresting positive integer is interesting by itself. Contradiction!

A: Zero.

Q: Why?

A: Because all poles are in Eastern Europe!

A: Zorn's lemon...

His classmate calms him down: "Nobody will be able to trace my homework to you: I'll be changing the names of all the constants and variables: a to b, x to y, etc."

Not quite convinced, but eager to be left alone, the student hands his completed assignment to the classmate for copying. After the deadline, the student asks: "Did you really change the names of all the variables?"

"Sure!" the classmate replies. "When you called a function f, I called it g; when you called a variable x, I renamed it to y; and when you were writing about the log of x+1, I called it the timber of x+1..."

A: An abelian grape...

When the winning ticket is drawn, and the jubilant winner comes to claim his prize, the mathematician explains the mode of payment: "1 dollar now, 1/2 dollar next week, 1/3 dollar the week after that..."

Personally I don't like this joke, math people usually have to spend more time in research than the others, but didn't get that much return/payoff as the people in the other areas.

A: When you have to multiply, all you need are a log table and an adder!

A: Differentiate a log fire!

"What's your favorite thing about mathematics?" the brother wants to know.

"Knot theory."

"Yeah, me neither."

"It is precisely 60 million and three years, two months, and eighteen days old."

"How can you know that with such precision?!"

"Well, when I started working here, one of the scientists told me that the skeleton was 60 million years old - and that was precisely three years, two months, and eighteen days ago..."

"Well, it's a really hard problem: There are four ducks swimming in a pond, when two more ducks come and join them. How many ducks are now swimming in the pond?"

The professor stares at his son with disbelief: "You couldn't do that?! All you need to know is that 4 + 2 = 6!"

"Do you think, I'm stupid?! Of course, I know that 4 + 2 = 6. But what does this have to do with ducks!?"

A mathematician: "Pi is the ratio of the circumference of a circle to its diameter."

A computer programmer: "Pi is 3.141592653589 in double precision."

A physicist: "Pi is 3.14159 plus or minus 0.000005."

An engineer: "Pi is about 22/7."

A nutritionist: "Pie is a healthy and delicious dessert!"