It’s Back to Prime Time

March 19, 2012 at 8:48 am Leave a comment

On Saturday, I turned 41 years old. I’ve been looking forward to this for a while. It’s a prime year, and its twin prime is two years away. In between, I’ll be a number of years that is “the answer to life, the universe, and everything.”

Forty-one is also cool because f(x) = x2 + x + 41 is a prime-generating function. That is, f(1) = 43, f(2) = 47, f(3) = 53, and so on.

What is the first value of x for which x2 + x + 41 is not prime?

The following image might help you answer that question. The number 41 appears in the center, and consecutive positive integers then proceed in a spiral. Notice that all of the numbers highlighted in yellow are prime. A pattern of primes continues along the diagonal — at least for a little while.

41 Spiral

It also turns out that 41 is the smallest number whose cube is the sum of three cube numbers in two different ways:

413 = 23 + 173 + 403 = 63 + 323 + 333 = 68,921

And 41 is the sum of the first six prime numbers:

2 + 3 + 5 + 7 + 11 + 13 = 41

At 41, I still feel young. But you know you’re an old mathematician when…

  • You report your age in hexadecimal. (I’m only 29!)
  • You’re not dead, but you’ve lost most of your functions.
  • The distance you walked to school as a kid is directly proportional to your age.
  • Your age can be described as “countably infinite.”
  • You regularly go off on tangents.
  • The phrase “pulling an all nighter” means not getting up to pee.
  • When asked your age, you reply, “I’m in the 99th percentile.”
  • You use the term surd, and you know how to calculate its value on a slide rule.
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About MJ4MF

The Math Jokes 4 Mathy Folks blog is an online extension to the book Math Jokes 4 Mathy Folks. The blog contains jokes submitted by readers, new jokes discovered by the author, details about speaking appearances and workshops, and other random bits of information that might be interesting to the strange folks who like math jokes.

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Math Jokes 4 Mathy Folks is available from Amazon, Borders, Barnes & Noble, NCTM, Robert D. Reed Publishers, and other purveyors of exceptional literature.

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