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%I #14 Dec 15 2018 06:29:24
%S 1,1,21,331,6181,116601,2248575,43874139,864287973,17148949027,
%T 342237634221,6862175029689,138132246844879,2789732439723061,
%U 56501091296763855,1147129435985083731,23339695295337149925,475767618472211229549
%N Number of arrays of n integers in -10..10 with sum zero.
%H Seiichi Manyama, <a href="/A322540/b322540.txt">Table of n, a(n) for n = 0..300</a>
%F a(n) = [x^(10*n)] (Sum_{k=0..20} x^k)^n.
%F a(n) ~ sqrt(3) * 21^n / (2*sqrt(55*Pi*n)). - _Vaclav Kotesovec_, Dec 15 2018
%t 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 (PARI) {a(n) = polcoeff((sum(k=0, 20, x^k))^n, 10*n, x)}
%Y Column 10 of A201552.
%K nonn
%O 0,3
%A _Seiichi Manyama_, Dec 14 2018
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