A joke proof of a famous mathematician showing that a certain two-digit number is prime

Question

There was a joke (highly sophisticated, non-elementary) proof of a famous mathematician showing that a certain two-digit number (like 43 or 83 but I forgot what) is prime. Could you remind me of a number/mathematician or provide a link?

Answer 1

There is a famous story about Alexander Grothendieck, one of the foremost mathematicians of the second half of the twentieth century:

One striking characteristic of Grothendieck’s mode of thinking is that it seemed to rely so little on examples. This can be seen in the legend of the so-called “Grothendieck prime”. In a mathematical conversation, someone suggested to Grothendieck 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 suggested, “All right, take 57.”

(Allyn Jackson “Comme Appelé du Néant—As if Summoned from the Void: The Life of Alexandre Grothendieck”, part 2. Notices of the AMS, 51 #10, Nov. 2004, p.1196.)