November 13, 2015, when expressed in MM/DD/YY format, is 11/13/15. The MM, DD and YY terms, in that order, form an arithmetic progression. It is non-trivial because the three numbers are different.

The first such date in any given century is 01/02/03. What is the last non-trivial arithmetic progression in the century?

What is the last non-trivial geometric progression in the century?

(In reply to answers revisited by Ady TZIDON)

OK, now the hats can be handed out!  Congratulations to Ady and Charlie, each of whom solved half the puzzle.

Posted by Steve Herman on 2015-11-17 20:09:46