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A342432
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a(n) = Sum_{k=1..n} gcd(k,n)^(n-2).
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5
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1, 2, 5, 22, 129, 1411, 16813, 266372, 4787349, 100391653, 2357947701, 61980047702, 1792160394049, 56707753687079, 1946197516142925, 72061992621375496, 2862423051509815809, 121441389759089405193, 5480386857784802185957
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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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a(n) = Sum_{d|n} phi(n/d) * d^(n-2).
a(n) = Sum_{d|n} mu(n/d) * d * sigma_(n-3)(d).
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MATHEMATICA
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a[n_] := Sum[GCD[k, n]^(n - 2), {k, 1, n}]; Array[a, 20] (* Amiram Eldar, Mar 12 2021 *)
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PROG
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(PARI) a(n) = sum(k=1, n, gcd(k, n)^(n-2));
(PARI) a(n) = sumdiv(n, d, eulerphi(n/d)*d^(n-2));
(PARI) a(n) = sumdiv(n, d, moebius(n/d)*d*sigma(d, n-3));
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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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