July 2015 Fiendish Function

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

• GUESS
• REPLY
• 1
• 7
• 2
• 5
• 3
• 1
• 4
• 83
• 5
• 67
• 10
• 8975

The rule was: "Multiply this number of twos together, then convert each digit to 9 minus the digit".

Suppose the guess was 13:

• Raise two to this power, giving 8192.
• Convert each digit to 9 minus the digit, giving 1807.

So the result is 1807.