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

Author

Jonathan Vos Post, Feb 15 2005

Keywords

• easy
• nonn

Crossrefs

Cf. A001358, A103378, A103388.

Programs

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 *)

Formula

Intersection of A103378 with A001358.

Extensions

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

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