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A295521
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a(n) = (1/n) * Sum_{d|n} mu(n/d)*(4^d - 3^d - 2^d + 1).
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2
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0, 2, 10, 39, 150, 545, 2010, 7320, 26880, 98775, 365010, 1353185, 5038950, 18830145, 70623958, 265737270, 1002976350, 3796197160, 14406059010, 54801140307, 208932573650, 798218035245, 3055417070010, 11716354754030, 45002103387120, 173117601112575
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OFFSET
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1,2
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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/#] * (4^# - 3^# - 2^# + 1) &] / n; Array[a, 26] (* Amiram Eldar, Oct 04 2023 *)
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PROG
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(PARI) {a(n) = sumdiv(n, d, moebius(n/d)*(4^d-3^d-2^d+1))/n}
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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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