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

1,1

Comments

Intersection of A103375 with A001358.

Links

Table of n, a(n) for n=1..33.

Example

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.

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]]

Crossrefs

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

Sequence in context: A103398 A103397 A103394 * A103393 A103392 A073046

Adjacent sequences: A103392 A103393 A103394 * A103396 A103397 A103398

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