A103398 Semiprimes in A103378.

4, 9, 15, 21, 33, 38, 58, 65, 86, 106, 121, 129, 265, 511, 2047, 2049, 4109, 16293, 16489, 17855, 19857, 32678, 34709, 66217, 104739, 220918, 240367, 262298, 293323, 954413, 2082999, 3145729, 3498467, 4296813, 16442015, 18037939, 21317326

Offset

1,1

Links

Table of n, a(n) for n=1..37.

Formula

Intersection of A103378 with A001358.

Maple

A103378 := proc(n) option remember; if n <= 11 then 1 ; else procname(n-10)+procname(n-11) ; fi ; end proc:
a78prev := -1 ; for n from 1 to 400 do a78 := A103378(n) ; if numtheory[bigomega](a78) = 2 and a78 <> a78prev then printf("%d, ", a78) ; end if; a78prev := a78 ; end do: # R. J. Mathar, Jun 11 2010

Mathematica

SemiprimeQ[n_]:=Plus@@FactorInteger[n][[All, 2]]?2; Clear[a]; k=10; Do[a[n]=1, {n, k+1}]; a[n_]:=a[n]=a[n-k]+a[n-k-1]; A103377=Array[a, 100] A103387=Union[Select[Array[a, 1000], PrimeQ]] A103397=Union[Select[Array[a, 300], SemiprimeQ]] N[Solve[x^11 - x - 1 == 0, x], 111][[2]] (* Ray Chandler and Robert G. Wilson v *)

Crossrefs

Cf. A001358, A103378, A103388.

Sequence in context: A103396 A103400 A103399 * A103397 A103394 A103395

Adjacent sequences: A103395 A103396 A103397 * A103399 A103400 A103401

Keyword

easy,nonn

Author

Jonathan Vos Post, Feb 15 2005

Extensions

Edited and extended by Ray Chandler and Robert G. Wilson v

Entries >511 corrected by R. J. Mathar, Jun 11 2010

Status

approved