A127018 Least s with s, t both semiprime and s+2n = t.

4, 6, 4, 6, 4, 9, 21, 6, 4, 6, 4, 9, 9, 6, 4, 6, 4, 10, 39, 6, 4, 14, 9, 9, 15, 6, 4, 6, 4, 9, 15, 10, 21, 6, 4, 10, 21, 6, 4, 6, 4, 9, 9, 6, 4, 14, 21, 10, 21, 6, 4, 14, 9, 10, 9, 6, 4, 6, 4, 9, 21, 9, 15, 6, 4, 9, 9, 6, 4, 6, 4, 14, 9, 10, 9, 6, 4, 10, 25, 6, 4, 14, 21, 9, 15, 6, 4, 9, 9, 14, 21, 10

Offset: 1

Author

Rick L. Shepherd, Jan 02 2007

Keywords

• nonn

Crossrefs

Cf. A001358, A127019, A020483.

Programs

Mathematica

sp=Select[Range[1000],PrimeOmega[#]==2&];seq={};Do[s=0;Until[PrimeOmega[sp[[s]]+2n]==2,s++];AppendTo[seq,sp[[s]]],{n,92}];seq (* James C. McMahon, Dec 30 2024 *)

PARI

a(n) = for (k=1, oo, if ((bigomega(k)==2) && bigomega(2*n+k)==2, return(k))); \\ Michel Marcus, Dec 30 2024