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 A218172 #17 May 11 2017 18:19:25
%S A218172 121,253,793,1261,1441,1633,1837,2773,3601,3901,4213,4537,4873,5221,
%T A218172 7141,9841,11881,14113,14701,16537,17173,17821,19153,19837,21241,
%U A218172 22693,23437,24193,24961,28153,28981,29821,30673,34201,37921,38881,39853,40837,41833,43861,45937,48061,49141,50233,53581,55873
%N A218172 Centered 12-gonal numbers which are semiprimes, intersection of A003154 and A001358.
%C A218172 Might also be called 'semiprime star numbers'.
%C A218172 A083749 and A006061 are subsequences.
%H A218172 Zak Seidov, <a href="/A218172/b218172.txt">Table of n, a(n) for n = 1..1000</a>
%e A218172 a(1) = 121 = 11^2 = A001358(40) = A003154(5) = A083749(1) = A006061(1) = A078972(11).
%e A218172 a(2) = 253 = 11*23 = A001358(81) = A003154(7) = A083749(2) = A078972(18).
%t A218172 Select[Table[6n(n-1)+1,{n,100}],PrimeOmega[#]==2&] (* _Harvey P. Dale_, Sep 01 2014 *)
%o A218172 (PARI) lista(nn) = {for (n = 1, nn, if (bigomega(v = 6*n*(n-1) + 1) == 2, print1(v, ", ")););} \\ _Michel Marcus_, Nov 09 2013
%Y A218172 Cf. A003154, A001358, A006061, A078972, A083749.
%K A218172 nonn
%O A218172 1,1
%A A218172 _Zak Seidov_, Oct 22 2012