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A268617
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a(n) = (1/n^2) * Sum_{d|n} moebius(n/d)*binomial(3*d,d).
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3
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3, 3, 9, 30, 120, 513, 2373, 11484, 57861, 300420, 1599477, 8692074, 48061689, 269694453, 1532744100, 8808000696, 51110965698, 299155382325, 1764498529977, 10479611189400, 62629105220514, 376411503694677, 2273982941083533, 13802537605619124, 84141675425838225, 514987312014416553, 3163620641291970255
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OFFSET
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1,1
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COMMENTS
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2*a(n) is divisible by n (cf. A268618).
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LINKS
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FORMULA
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MATHEMATICA
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a[n_] := DivisorSum[n, MoebiusMu[n/#] * Binomial[3*#, #] &] / n^2; Array[a, 30] (* Amiram Eldar, Aug 24 2023 *)
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PROG
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(PARI) { a(n) = sumdiv(n, d, moebius(n/d)*binomial(3*d, d))/n^2; }
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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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