A103392 Semiprimes in A103372.

4, 9, 15, 21, 33, 38, 58, 86, 106, 122, 485, 905, 1939, 4163, 6697, 12381, 14473, 22889, 107833, 170769, 370729, 687634, 804106, 1093762, 1276259, 2767999, 11140379, 15186449, 210634829, 286937249, 391048473, 532793518, 725995178, 847539571

Offset: 1

Author

Jonathan Vos Post, Feb 03 2005

Keywords

• nonn
• easy

Comments

Intersection of A103372 with A001358.

Examples

			276799 is an element of this sequence because A103372(99) = 276799 and 276799 is semiprime because 276799 = 31 * 8929 where both 31 and 8929 are primes.
		

Crossrefs

Cf. A001358, A103372, A103382, A103393-A103401.

Programs

Mathematica

SemiprimeQ[n_] := Plus @@ FactorInteger[n][[All, 2]] == 2; k = 4; Do[a[n] = 1, {n, k + 1}]; a[n_] := a[n] = a[n - k] + a[n - k - 1]; Union[Select[Array[a, 150], SemiprimeQ]]
Union[Select[LinearRecurrence[{0,0,0,1,1},{1,1,1,1,1},150],PrimeOmega[#] == 2&]] (* Harvey P. Dale, Apr 22 2015 *)

Extensions

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