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A354891
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a(n) = n! * Sum_{d|n} d^(n - d) / d!.
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6
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1, 3, 7, 73, 121, 9721, 5041, 1760641, 44452801, 562615201, 39916801, 3156125575681, 6227020801, 192873372531841, 222245415808416001, 14806216643368550401, 355687428096001, 34884164976924636172801, 121645100408832001
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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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E.g.f.: Sum_{k>0} x^k/(k! * (1 - (k * x)^k)).
If p is prime, a(p) = 1 + p! = A038507(p).
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MATHEMATICA
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a[n_] := n! * DivisorSum[n, #^(n - #)/#! &]; Array[a, 19] (* Amiram Eldar, Jun 10 2022 *)
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PROG
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(PARI) a(n) = n!*sumdiv(n, d, d^(n-d)/d!);
(PARI) my(N=20, x='x+O('x^N)); Vec(serlaplace(sum(k=1, N, x^k/(k!*(1-(k*x)^k)))))
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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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