February 2017 Fiendish Function

The Fiendish Function posed during February 2017 had the following sample guesses and replies:

  • GUESS
  • REPLY
  • 1
  • 5
  • 2
  • 10
  • 3
  • 26
  • 4
  • 50
  • 5
  • 122
  • 10
  • 842

The rule was: "The nth prime, square it, then add one".

Suppose the guess was 11:

  • Find the eleventh prime, giving 31.
  • Multiply the number by itself, giving 961.
  • Add one, giving 962.

So the result is 962.