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 A262749 #18 Dec 26 2015 18:41:44
%S A262749 16,31,46,51,76,81,94,106,111,121,123,126,133,141,146,156,157,172,174,
%T A262749 181,186,191,196,198,211,216,225,226,231,237,241,246,256,259,268,276,
%U A262749 281,286,289,291,297,301,310,315,321,326,328,331,336,346,354,361,366
%N A262749 Numbers that are the sum of two distinct nonzero triangular numbers in more than one way.
%C A262749 The magic sum of any 3 X 3 semimagic square composed of triangular numbers is a(n) + A000217(m) for some m and n.
%e A262749 16 = 1 + 15 = 6 + 10.
%t A262749 r = 366; lst = Table[0, {r}]; lim = Floor[Sqrt[8*r - 7]]; Do[num = (i^2 + i)/2 + (j^2 + j)/2; If[num <= r, lst[[num]]++], {i, lim}, {j, i - 1}]; Flatten@Position[lst, n_ /; n > 1]
%t A262749 Module[{nn=30,trnos},trnos=Accumulate[Range[nn]];Select[Sort[Flatten[ Table[ PositionIndex[Counts[Total/@Subsets[trnos,{2}]]][i],{i,2,nn}]]], #<= Last[trnos]&]] (* The program uses the PositionIndex and Counts functions from Mathematica version 10 *) (* _Harvey P. Dale_, Dec 26 2015 *)
%Y A262749 Cf. A000217, A051533, A260647, A265140 (exactly one way), A265134 (exactly two ways), A265135 (more than two ways), A265136 (exactly three ways), A265137 (more than three ways), A265138 (exactly four ways).
%K A262749 nonn
%O A262749 1,1
%A A262749 _Arkadiusz Wesolowski_, Dec 02 2015