Strong pseudoprime - Wikipedia
https://en.wikipedia.org/wiki/Strong_pseudoprimeA strong pseudoprime is a composite number that passes the Miller–Rabin primality test. All prime numbers pass this test, but a small fraction of composites also pass, making them "pseudoprimes". Unlike the Fermat pseudoprimes, for which there exist numbers that are pseudoprimes to all coprime bases (the Carmichael numbers), there are no composites that are strong pseudoprim…
Online calculator: Fermat primality test
https://planetcalc.com/8983The calculator tests an input number by a primality test based on Fermat's little theorem. Using this calculator, you can find if an input number is Fermat pseudoprime. The calculator uses the Fermat primality test, based on Fermat's little theorem. If n is a prime number, and a is not divisible by n, then : .