August 2016 Fiendish Function

The Fiendish Function posed during August 2016 had the following sample guesses and replies:

• GUESS
• REPLY
• 1
• 2
• 2
• 4
• 3
• 8
• 4
• 7
• 5
• 5
• 10
• 7

The rule was: "Multiply this number of twos together, then add the digits together".

Suppose the guess was 13:

• Raise two to this power, giving 8192.
• Find the number's digits, giving 8, 1, 9, 2
• Add these together, giving 20.

So the result is 20.