A127018 - OEIS

%I #9 Dec 30 2024 12:52:54

%S 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,

%T 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,

%U 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

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

%t 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 *)

%o (PARI) a(n) = for (k=1, oo, if ((bigomega(k)==2) && bigomega(2*n+k)==2, return(k))); \\ _Michel Marcus_, Dec 30 2024

%Y Cf. A001358, A127019, A020483.

%K nonn

%O 1,1

%A _Rick L. Shepherd_, Jan 02 2007