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?
Not so fast... we'll slow down!
ok, there was no year 00 AD so 2000 still belongs to 20th century:
12/06/00 is the last ar. seq. d=-6
08/28/98 is the last geo. seq. q=7/2
Meglio tardi che mai,