1251949

Appears in sequences

• Sarrus numbers k such that k-1 and k+1 have the same number of prime divisors (counted with multiplicity).at n=12A086806
• Overpseudoprimes to base 2: composite k such that k = A137576((k-1)/2).at n=29A141232
• a(n) is the least base-2 overpseudoprime k such that the multiplicative order of 2 mod k equals 8*n+20.at n=22A141629
• Strong pseudoprimes (base 2) that become prime when two is subtracted.at n=11A230483
• Strong pseudoprimes k to base 2 such that either k-2 or k+2 is prime.at n=15A230487
• Composite numbers k congruent to 5 (mod 8) such that 2^((k-1)/2) mod k = k-1.at n=14A244626
• The "non-residue" pseudoprimes: odd composite numbers n such that b(n)^((n-1)/2) == -1 (mod n), where base b(n) = A020649(n).at n=22A307767
• Numbers k such that 2^(k-1) == 1 (mod k) and lpf(k)-1 does not divide k-1.at n=29A316906
• Numbers k such that 2^(k-1) == 1 (mod k) and p-1 does not divide k-1 for every prime p dividing k.at n=26A316907
• Odd composite numbers k such that 2^((k-1)/2) == -1 (mod k).at n=16A356638