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 A249564 #14 Aug 24 2023 09:48:50
%S A249564 1,1,10,244,11378,867395,98204132,15475158552,3239399341956,
%T A249564 869652788703285,291315412833808702,119114020598815073524,
%U A249564 58386684085633233147478,33797341113242898165287495,22810507257314647778044971848,17755122836243141585656207243952
%N A249564 a(n) = Sum_{k = 0..n} (k*(k+1)/2)^n.
%H A249564 Vaclav Kotesovec, <a href="/A249564/b249564.txt">Table of n, a(n) for n = 0..200</a>
%F A249564 E.g.f.: Sum_{n>=0} exp(x*n*(n+1)/2).
%F A249564 a(n) ~ exp(3) * n^(2*n) / ((exp(2)-1) * 2^n).
%t A249564 Table[n!*SeriesCoefficient[Sum[Exp[x*k*(k+1)/2], {k, 0, n}], {x, 0, n}], {n, 0, 20}]
%t A249564 Flatten[{1,Table[Sum[(k*(k+1)/2)^n,{k,1,n}],{n,1,20}]}]
%o A249564 (PARI) a(n) = sum(k=0, n, (k*(k+1)/2)^n); \\ _Michel Marcus_, Aug 24 2023
%Y A249564 Cf. A000217, A031971, A177385.
%K A249564 nonn,easy
%O A249564 0,3
%A A249564 _Vaclav Kotesovec_, Nov 01 2014
%E A249564 New name from _Peter Bala_, Aug 18 2023