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A244036
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a(n) = Sum_{d|n} Sum{t|d} (n/d)*moebius(d/t)*binomial(3*t,t)/(3*d^2).
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0
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1, 3, 6, 16, 45, 186, 798, 3860, 19305, 100235, 533170, 2897760, 16020576, 89899754, 510914850, 2936007952, 17036988583, 99718499907, 588166176678, 3493203930320, 20876368409253, 125470502297910, 757994313694534, 4600845874346712, 28047225141946300, 171662437370180016
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OFFSET
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1,2
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LINKS
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MAPLE
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with(numtheory);
f:=proc(N) local Na, n, ans;
ans:=0;
for Na in divisors(N) do
for n in divisors(Na) do
ans := ans + (N/Na)*mobius(Na/n)*binomial(3*n, n)/(3*Na^2); od: od:
ans;
end;
[seq(f(n), n=1..30)];
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MATHEMATICA
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a[n_] := Sum[(n/d) MoebiusMu[d/t] Binomial[3t, t]/(3d^2), {d, Divisors[n]}, {t, Divisors[d]}];
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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