A103395 Semiprimes in A103375.

4, 9, 15, 21, 33, 38, 58, 65, 86, 106, 121, 129, 265, 2049, 3865, 4163, 8557, 14005, 80413, 104757, 116333, 152713, 241354, 2273893, 2492909, 16432401, 31701485, 34090613, 263504954, 424792297, 1534443805, 3233454667, 10580401481

Offset: 1

Author

Jonathan Vos Post, Feb 03 2005

Keywords

• nonn
• easy

Comments

Intersection of A103375 with A001358.

Examples

			14005 is an element of this sequence because A103375(106) = 14005 and
14005 is semiprime because 14005 = 5 * 2801 where both 5 and 2801 are primes. It is coincidence here that 106 = 2 * 53 is also semiprime.
		

Crossrefs

Cf. A001358, A103375, A103385, A103392-A103401.

Programs

Mathematica

SemiprimeQ[n_] := Plus @@ FactorInteger[n][[All, 2]] == 2; k = 7; Do[a[n] = 1, {n, k + 1}]; a[n_] := a[n] = a[n - k] + a[n - k - 1]; Union[Select[Array[a, 255], SemiprimeQ]]

Extensions

Edited, corrected and extended by Ray Chandler and Robert G. Wilson v, Feb 06 2005