1,1

a(1) = 25 because A056106(3) = 3*3^2 - 3 + 1 = 25 = 5^2 is semiprime. A056106(4) = 3*4^2 - 4 + 1 = 45 = 3^2 * 5 is not in the sequence, as it is a 3-almost prime. A056106(5) = 3*5^2 - 5 + 1 = 71 is not in the sequence, as it is a prime. a(36) = 29901 because A056106(100) = 3*100^2 - 100 + 1 = 29901 = 3 * 9967 is semiprime.

{a(n)} = {3*n^2 - n + 1 iff semiprime}. {a(n)} = A056106 INTERSECT A001358.

Cf. A001358, A056106.

Sequence in context: A042216 A042218 A045166 this_sequence A072471 A017042 A100255

Adjacent sequences: A113521 A113522 A113523 this_sequence A113525 A113526 A113527

easy,nonn

Jonathan Vos Post (jvospost2(AT)yahoo.com), Jan 12 2006