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A103393 Semiprimes in A103373. 3
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Intersection of A103373 with A001358.

LINKS

Table of n, a(n) for n=1..36.

EXAMPLE

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.

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 *)

CROSSREFS

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

Sequence in context: A103397 A103394 A103395 * A103392 A073046 A066495

Adjacent sequences:  A103390 A103391 A103392 * A103394 A103395 A103396

KEYWORD

nonn,easy

AUTHOR

Jonathan Vos Post, Feb 03 2005

EXTENSIONS

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

STATUS

approved

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Last modified May 9 19:47 EDT 2021. Contains 343746 sequences. (Running on oeis4.)