1,1

{a(n)} = {3*n^2 - 2*n + 1 iff semiprime}. {a(n)} = A056105 INTERSECT A001358.

A056105(44) = 3*44^2 - 2*44 + 1 = 5721 = 3 * 1907 which is a semiprime.

A056105(24) = 3*24^2 - 2*24 + 1 = 1681 = 41^2 which is a semiprime (the two prime factors need not be distinct).

A056105(100) = 3*100^2 - 2*100 + 1 = 29801 = 17 * 1753, which is a semiprime.

41 is not in this sequence because A056105(4) = 41 is prime.

3009 is not in this sequence because A056105(32) = 3009 = 3 * 17 * 59 is a 3-almost prime.

Cf. A001358, A056105.

Sequence in context: A130861 A049730 A131895 this_sequence A123833 A084023 A156342

Adjacent sequences: A113516 A113517 A113518 this_sequence A113520 A113521 A113522

easy,nonn

Jonathan Vos Post (jvospost3(AT)gmail.com), Jan 12 2006