# Thread: Find a prime factor of 99!-1

1. ## Find a prime factor of 99!-1

Find a prime factor of 99!-1

2. Originally Posted by cornoth
Find a prime factor of 99!-1
101, because 101 is prime and $99! \equiv -100! \equiv 1$ in $Z_{101}$

3. oh thats right, wilson's theorem.
thanks hpe!