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 A322540 #18 Oct 19 2024 16:17:07
%S A322540 1,1,21,331,6181,116601,2248575,43874139,864287973,17148949027,
%T A322540 342237634221,6862175029689,138132246844879,2789732439723061,
%U A322540 56501091296763855,1147129435985083731,23339695295337149925,475767618472211229549,9714486212587875804351
%N A322540 Number of arrays of n integers in -10..10 with sum zero.
%H A322540 Seiichi Manyama, <a href="/A322540/b322540.txt">Table of n, a(n) for n = 0..300</a>
%F A322540 a(n) = [x^(10*n)] (Sum_{k=0..20} x^k)^n.
%F A322540 a(n) ~ sqrt(3) * 21^n / (2*sqrt(55*Pi*n)). - _Vaclav Kotesovec_, Dec 15 2018
%p A322540 seq(add((-1)^k*binomial(n, k)*binomial(11*n-21*k-1, n-1), k = 0..floor(n/2)), n = 0..20); # _Peter Bala_, Oct 19 2024
%t A322540 a[n_] := If[n==0, 1, Coefficient[Expand[Sum[x^k, {k, 0, 20}]^n], x^(10n)]]; Array[a, 25, 0] (* _Amiram Eldar_, Dec 14 2018 *)
%o A322540 (PARI) {a(n) = polcoeff((sum(k=0, 20, x^k))^n, 10*n, x)}
%Y A322540 Column 10 of A201552.
%K A322540 nonn
%O A322540 0,3
%A A322540 _Seiichi Manyama_, Dec 14 2018