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 A209309 #18 Aug 12 2023 04:36:19
%S A209309 6,12,18,24,48,54,96,102,110,114,138,162,174,186,192,204,220,222,228,
%T A209309 246,258,282,315,318,348,354,364,366,372,384,402,414,426,438,440,444,
%U A209309 456,474,486,492,498,516,522,534,550,558,564,582,606,618,636,642,654,678
%N A209309 Numbers whose sum of triangular divisors is also triangular and greater than 1.
%H A209309 Antonio Roldán, <a href="/A209309/b209309.txt">Table of n, a(n) for n = 1..8055</a> (terms <= 10^5)
%e A209309 186 is a term because the sum of its triangular divisors, 1+3+6 = 10 is also triangular.
%t A209309 triQ[n_] := n > 1 && IntegerQ[Sqrt[8*n+1]]; q[n_] := triQ[1 + DivisorSum[n, #&, triQ[#] &]]; Select[Range[700], q] (* _Amiram Eldar_, Aug 12 2023 *)
%o A209309 (PARI) istriangular(n)=issquare(8*n+1)
%o A209309 {t=0; for(n=1, 10^5, k=sumdiv(n, d, istriangular(d)*d); if(istriangular(k)&&k>>1, t+=1; write("b209309.txt",t," ",n)))}
%Y A209309 Cf. A000217, A035316, A185027, A209310.
%K A209309 nonn
%O A209309 1,1
%A A209309 _Antonio Roldán_, Jan 18 2013