5590621domain: NAppears in sequencesStrong pseudoprimes (base 2) that become prime when two is subtracted.at n=21A230483Strong pseudoprimes k to base 2 such that either k-2 or k+2 is prime.at n=29A230487Composite numbers k congruent to 5 (mod 8) such that 2^((k-1)/2) mod k = k-1.at n=31A244626