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

1,1

Comments

Intersection of A103372 with A001358.

Links

Table of n, a(n) for n=1..34.

Example

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.

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 *)

Crossrefs

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

Sequence in context: A103394 A103395 A103393 * A073046 A066495 A313298

Adjacent sequences: A103389 A103390 A103391 * A103393 A103394 A103395

Keyword

nonn,easy

Author

Jonathan Vos Post, Feb 03 2005

Extensions

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

Status

approved