Your task as cops is to select three things:
A programming language
An OEIS sequence
A byte set
You are then to secretly write a program in that language that computes the nth term sequence using only the bytes in the set. You will reveal the three pieces of information so that robbers can try to figure out the program.
Answers will be scored by the number of bytes in the byte set with more score being good. Cracked answers have an automatic score of 0. If your answer is uncracked after one week you may reveal the intended program and mark your answer as "safe".
Answers must be capable of calculating every term in the b-files of the sequence, but are not required to calculate any terms after.
Sequences can be either 1 or 0 indexed for both cops and robbers.
Here is a Python Script that checks if your code matches the given byte set.