March 2018 Fiendish Function

The Fiendish Function posed during March 2018 had the following sample guesses and replies:

  • GUESS
  • REPLY
  • 1
  • 2
  • 2
  • 2
  • 3
  • 4
  • 4
  • 2
  • 5
  • 6
  • 10
  • 6

The rule was: "Write the number in binary, reverse it, and then convert it back to decimal, then add one".

Suppose the guess was 25:

  • Write this in binary, giving 11001.
  • Reverse it, giving 10011
  • Convert this back to decimal, giving 19.
  • Add one, giving 20.

So the result is 20.