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%I #16 Mar 20 2019 13:16:54
%S 1,3,6,16,45,186,798,3860,19305,100235,533170,2897760,16020576,
%T 89899754,510914850,2936007952,17036988583,99718499907,588166176678,
%U 3493203930320,20876368409253,125470502297910,757994313694534,4600845874346712,28047225141946300,171662437370180016
%N a(n) = Sum_{d|n} Sum{t|d} (n/d)*moebius(d/t)*binomial(3*t,t)/(3*d^2).
%H M. Isachenkov, I. Kirsch, V. Schomerus, <a href="http://arxiv.org/abs/1403.6857">Chiral Primaries in Strange Metals</a>, arXiv preprint arXiv:1403.6857 [hep-th], 2014. See display following (3.5).
%p with(numtheory);
%p f:=proc(N) local Na, n, ans;
%p ans:=0;
%p for Na in divisors(N) do
%p for n in divisors(Na) do
%p ans := ans + (N/Na)*mobius(Na/n)*binomial(3*n,n)/(3*Na^2); od: od:
%p ans;
%p end;
%p [seq(f(n),n=1..30)];
%t a[n_] := Sum[(n/d) MoebiusMu[d/t] Binomial[3t, t]/(3d^2), {d, Divisors[n]}, {t, Divisors[d]}];
%t Array[a, 26] (* _Jean-François Alcover_, Dec 06 2017, from Maple *)
%K nonn
%O 1,2
%A _N. J. A. Sloane_, Jun 28 2014
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