A103393 Semiprimes in A103373.

4, 9, 15, 21, 33, 38, 58, 65, 86, 106, 121, 249, 895, 989, 1199, 2059, 3073, 9206, 12302, 19766, 33238, 63109, 197459, 252982, 283942, 477931, 691357, 4598261, 8671301, 9819097, 11176233, 51113687, 205150267, 232797043, 496450043, 562358905

Offset: 1

Author

Jonathan Vos Post, Feb 03 2005

Keywords

• nonn
• easy

Comments

Intersection of A103373 with A001358.

Examples

			63109 is an element of this sequence because A103373(91) = 63109 and 63109 is semiprime because 63109 = 223 * 283 where both 223 and 283 are primes.
		

Crossrefs

Cf. A001358, A103373, A103383, A103392-A103401.

Programs

Mathematica

SemiprimeQ[n_] := Plus @@ FactorInteger[n][[All, 2]] == 2; k = 5; Do[a[n] = 1, {n, k + 1}]; a[n_] := a[n] = a[n - k] + a[n - k - 1]; Union[Select[Array[a, 170], SemiprimeQ]]
Select[LinearRecurrence[{0,0,0,0,1,1},{1,1,1,1,1,1},200],PrimeOmega[ #] == 2&]//Union (* Harvey P. Dale, Jul 20 2019 *)

Extensions

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