## December 2017 Fiendish Function

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

- 1
- 2
- 2
- 101
- 3
- 122
- 4
- 10001
- 5
- 10202
- 10
- 1020101

The rule was: "Write the number in binary, square it, then add one".

Suppose the guess was 26:

- Write the number in binary, giving 11010.
- Multiply the number by itself, giving 121220100.
- Add one, giving 121220101.

So the result is 121220101.

## Earlier answers

Here are the answers to the Fiendish Functions posted in earlier months: