An Euler pseudoprime to the base b is a composite number n which satisfies b^((n - 1)/2) congruent ± 1 (mod n). The first few base-2 Euler pseudoprimes are 341, 561, 1105, 1729, 1905, 2047, ... (OEIS A006970).

Euler-Jacobi pseudoprime | pseudoprime | strong pseudoprime

Leonhard Euler