A103394 Semiprimes in A103374.

4, 9, 15, 21, 33, 38, 58, 65, 86, 106, 121, 129, 265, 979, 1079, 2279, 7985, 8491, 14019, 15397, 37606, 61289, 71845, 117013, 127401, 196763, 221905, 244414, 265358, 290111, 466319, 555469, 1065241, 1672598, 4276487, 4712791, 5266246, 8178897

Offset: 1

Author

Jonathan Vos Post, Feb 03 2005

Keywords

• nonn
• easy

Examples

			61289 is an element of this sequence because A103374(107) = 61289 and 61289 is semiprime because 61289 = 167 * 367 where both 167 and 367 are primes.
		

Crossrefs

Intersection of A103374 with A001358.

Cf. A001358, A103374, A103384, A103392-A103401.

Programs

Mathematica

SemiprimeQ[n_] := Plus @@ FactorInteger[n][[All, 2]] == 2; k = 6; Do[a[n] = 1, {n, k + 1}]; a[n_] := a[n] = a[n - k] + a[n - k - 1]; Union[Select[Array[a, 160], SemiprimeQ]]
Select[LinearRecurrence[{0,0,0,0,0,1,1},{1,1,1,1,1,1,1},200],PrimeOmega[#]==2&]//Union (* Harvey P. Dale, Sep 02 2024 *)

Extensions

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