In this cops-and-robbers challenge cops will think of a positive integer. They will then write a program or function that outputs one value when provided the number as input and another value for all other positive integer inputs. Cops will then reveal the program in an answer keeping the number a secret. Robbers can crack an answer by finding the number.
Here's the catch: this is not code-golf, instead your score will be the secret number with a lower score being better. Obviously you cannot reveal your score while robbers are still trying to find it. An answer that has not been cracked one week after its posting may have its score revealed and be marked safe. Safe answers cannot be cracked.
It probably goes without saying but you should be able to score your answer. That is you should know exactly what value is accepted by your decision machine. Simply knowing that there is one is not enough.
Use of Cryptographic functions
Unlike most cops and robbers challenge which ask you not to use cryptographic functions, this challenge not only entirely allows them but encourages them. You are free to create answers in any way as long as you are trying to win. That being said, answers using other methods are also welcome here. The goal of the challenge is to win, and as long as you don't cheat nothing is off the table.
Ais the Ackerman function. \$\endgroup\$