A122499 Semiprimes in A006053.

4, 9, 14, 155, 2993, 9707, 184183, 331981, 1942071, 1263047761, 140390505643, 455845099957, 296452328830865, 32951342156444219, 2381929669709247097441, 9063289616192276216577361, 34485996673867704851362967681, 426068342298911680872493712146539, 117190394374593808526426397401539675762247

Offset: 1

Author

Roger L. Bagula and Gary W. Adamson, Sep 15 2006

Keywords

• nonn

Crossrefs

Intersection of A001358 and A006053.

Cf. A006054.

Programs

Mathematica

SemiprimeQ[n_Integer] := Plus @@ (Last /@ FactorInteger[n]) == 2;
a = Table[ SeriesCoefficient[ Series[x/(x^3 - 2*x^2 - x + 1), {x, 0, 50}], n], {n, 0, 50}];
f[n_] = If[SemiprimeQ[a[[n]]] == True, a[[n]], {}];
Flatten[Table[f[n], {n, 1, Length[a]}]]

Extensions

Edited by N. J. A. Sloane, Sep 17 2006

More terms from Amiram Eldar, Jun 06 2025