There's an excellent quotation attributed to Alexandre Grothendieck, one of the greatest mathematicians alive. At a seminar he was giving on analytic number theory, someone suggested that they should consider a particular prime number. "You mean an actual number?" Grothendieck asked. The other person replied, yes, an actual prime number. Grothendieck replied "All right, take 57."
Is there a significance to 57 there?
57 isn't a prime number. 3 * 19 = 57
Yes, it isn't prime, that's the joke (I guess).
Yes, but not in the sense that Grothendieck made a joke by saying '57', but in the sense that Grothendieck, who knows quite a bit about prime numbers, said '57' without realizing that it is composite.
Yes, I understood it in this sense too :) Quite a character, Grothendieck.