November 2018 Fiendish Function

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

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

The rule was: "Write the number in binary, then add 2 to the power of the digits together".

Suppose the guess was 26:

• Write the number in binary, giving 11010.
• Take the number's digits, giving 1, 1, 0, 1, 0
• Take 2 to the power of each digit, giving 2, 2, 1, 2, 1
• Add these together, giving 8.

So the result is 8.