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 A022616 #13 Apr 05 2017 11:29:21
%S A022616 1,-21,210,-1351,6426,-24780,82845,-250806,703731,-1853481,4628337,
%T A022616 -11052867,25403952,-56451192,121738767,-255623851,524037507,
%U A022616 -1051143723,2066899387,-3990768663,7577013360,-14163858895
%N A022616 Expansion of Product_{m>=1} (1+q^m)^(-21).
%H A022616 Seiichi Manyama, <a href="/A022616/b022616.txt">Table of n, a(n) for n = 0..10000</a>
%F A022616 a(n) ~ (-1)^n * 7^(1/4) * exp(Pi*sqrt(7*n/2)) / (2^(7/4) * n^(3/4)). - _Vaclav Kotesovec_, Aug 27 2015
%F A022616 a(0) = 1, a(n) = -(21/n)*Sum_{k=1..n} A000593(k)*a(n-k) for n > 0. - _Seiichi Manyama_, Apr 05 2017
%t A022616 nmax = 50; CoefficientList[Series[Product[1/(1 + x^k)^21, {k, 1, nmax}], {x, 0, nmax}], x] (* _Vaclav Kotesovec_, Aug 27 2015 *)
%K A022616 sign
%O A022616 0,2
%A A022616 _N. J. A. Sloane_