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 A320848 #5 Oct 22 2018 11:04:45 %S A320848 1,1,2,3,4,5,7,9,10,12,14,16,18,20,22,24,26,29,32,34,36,39,42,45,48, %T A320848 51,54,57,60,63,66,69,73,77,80,83,86,89,93,97,101,105,109,112,116,120, %U A320848 124,128,132,136,140,145,150,154,158,162,166,170,174,179,184,189 %N A320848 Number of 2-element subsets of [n] whose sum is a triangular number. %H A320848 Alois P. Heinz, <a href="/A320848/b320848.txt">Table of n, a(n) for n = 2..10000</a> %Y A320848 Column k=2 of A284249. %Y A320848 Cf. A000217. %K A320848 nonn %O A320848 2,3 %A A320848 _Alois P. Heinz_, Oct 22 2018