May 2015 Fiendish Function

The Fiendish Function posed during May 2015 had the following sample guesses and replies:

  • GUESS
  • REPLY
  • 1
  • 1
  • 2
  • 8
  • 3
  • 9
  • 4
  • 10
  • 5
  • 8
  • 10
  • 1

The rule was: "Cube the number, then add the digits together".

Suppose the guess was 12:

  • Cube the number, giving 1728.
  • Find the number's digits, giving 1, 7, 2, 8
  • Add these together, giving 18.

So the result is 18.