A176004 (n-th prime > 3) minus (n-th semiprime).

1, 1, 2, 3, 3, 4, 2, 7, 6, 11, 8, 9, 12, 15, 20, 15, 18, 20, 18, 22, 25, 27, 32, 32, 29, 30, 27, 28, 41, 44, 46, 46, 55, 56, 51, 52, 52, 55, 60, 60, 69, 70, 68, 66, 77, 82, 85, 86, 88, 93, 86, 93, 98, 102, 103, 102, 100, 103, 100, 108, 120, 117, 112, 115, 128, 132, 141, 140, 140, 145

Offset: 1

Author

Juri-Stepan Gerasimov, Apr 11 2010, May 17 2010

Keywords

• nonn

Crossrefs

Cf. A168563.

Programs

Mathematica

Module[{nn=80,sem,len},sem=Select[Range[3*nn],PrimeOmega[#]==2&];len= Min[nn,Length[sem]];#[[1]]-#[[2]]&/@Thread[{Take[Prime[Range[ 3,nn+2]], len],Take[sem,len]}]] (* Harvey P. Dale, Sep 04 2015 *)

Formula

a(n)=prime(n+2)-semiprime(n).

Extensions

a(6) corrected by R. J. Mathar, Apr 16 2010

Corrected and extended by Harvey P. Dale, Sep 04 2015