September 2017 Fiendish Function

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

  • GUESS
  • REPLY
  • 1
  • 7
  • 2
  • 41
  • 3
  • 12
  • 4
  • 82
  • 5
  • 53
  • 10
  • 7

The rule was: "Multiply the number by seven, then reverse the order of the digits".

Suppose the guess was 12:

  • Multiply by seven, giving 84.
  • Reverse the order of the digits, giving 48.

So the result is 48.