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A103392 Semiprimes in A103372. 6
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified May 6 09:45 EDT 2021. Contains 343580 sequences. (Running on oeis4.)