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 A125215 #17 Dec 19 2019 05:37:18
%S A125215 9,15,21,39,69,111,129,309,381,489,501,771,879,939,1011,1299,1569,
%T A125215 2271,2391,2661,2859,3039,3189,3459,3849,3909,3921,4449,4791,4971,
%U A125215 5001,5079,5169,5349,5739,6009,6999,7041,7671,8691,8781,9201,10599,11469,11829
%N A125215 Semiprimes s such that s-/+2 are primes.
%C A125215 All terms are multiples of 3, a(n) = 3*A125272(n). - _Zak Seidov_, May 06 2013
%H A125215 Amiram Eldar, <a href="/A125215/b125215.txt">Table of n, a(n) for n = 1..10000</a>
%e A125215 9 = 3^2 is a term since it is a semiprime, and both 9 - 2 = 7 and 9 + 2 = 11 are primes.
%t A125215 Reap[Do[p=Prime[i];If[PrimeQ[p+4]&&Total[Last/@FactorInteger[p+2]]==2,Sow[p+2]],{i,2*10^3}]][[2,1]]
%Y A125215 Cf. A001358, A125272.
%K A125215 nonn
%O A125215 1,1
%A A125215 _Zak Seidov_, Nov 24 2006