221761domain: NAppears in sequencesStrong pseudoprimes to base 3.at n=32A020229Highly composite numbers + 1.at n=31A135372Overpseudoprimes to base 3.at n=16A141350Semiprime 12-gonal numbers.at n=13A380069a(n) = (n^2 - n + 2) * (5*n^2 - 5*n + 2) / 4.at n=20A380353