This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A209292 #18 Jan 17 2013 15:37:00
%S A209292 1,2,3,5,8,11,13,18,20,23,29,30,31,36,37,40,41,44,48,50,52,53,54,56,
%T A209292 63,67,68,73,75,76,78,81,83,89,90,96,97,98,99,103,105,112,113,114,116,
%U A209292 120,125,127,128,130,131,135,136,137,138,139,140,148,153,156
%N A209292 Non-semiprimes n such that 2n+1 are non-semiprimes.
%C A209292 This is to A005384 as nonsemiprimes A100959 are to primes A000040.
%F A209292 {n such that n is in A100959, and 2*n + 1 is in A100959} = {n such that n is not in A001358, and 2*n + 1 is not in A001358}.
%F A209292 a(n) ~ n. - _Charles R Greathouse IV_, Jan 16 2013
%e A209292 a(1) = 1 because 1 is not a semiprime (the smallest semiprime is 4), and 2*1 + 1 = 3 is not a semiprime.
%e A209292 7 is not a semiprime, but 2*7 + 1 = 15 = 3*5 is a semiprime, so 7 is not in this sequence.
%t A209292 SemiPrimeQ[n_Integer] := If[Abs[n] < 2, False, (2 == Plus @@ Transpose[FactorInteger[Abs[n]]][[2]])]; Select[Range[200], ! SemiPrimeQ[#] && ! SemiPrimeQ[2 # + 1] &] (* _T. D. Noe_, Jan 17 2013 *)
%o A209292 (PARI) is(n)=bigomega(n)!=2 && bigomega(2*n+1)!=2 \\ _Charles R Greathouse IV_, Jan 16 2013
%Y A209292 Cf. A001358, A005384, A100959, A209271.
%K A209292 nonn,easy
%O A209292 1,2
%A A209292 _Jonathan Vos Post_, Jan 16 2013