(n - 1)! + 1 is divisible by n if n is prime or 1
EDIT: therefore floor ( cos pi ((n-1)!+1)/n )² is a boolean prime detector :3
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it’s just part of willans’ formula, i just found it interesting
never heard of it (I’m in alg 2 rn, what course are you taking?)
Ayo I'm in the same one