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A336998
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a(n) = n! * Sum_{d|n} 3^(d - 1) / d!.
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1
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1, 5, 15, 87, 201, 3123, 5769, 148347, 913761, 11541123, 39975849, 2616723387, 6227552241, 230557039443, 4151870901369, 76980002233707, 355687471142721, 27886053280896963, 121645100796252489, 10474674957482235867, 135117295282596928401, 2811664555920692775603
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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>=1} (exp(3*x^k) - 1) / 3.
a(p) = p! + 3^(p - 1), where p is prime.
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MATHEMATICA
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Table[n! Sum[3^(d - 1)/d!, {d, Divisors[n]}], {n, 1, 22}]
nmax = 22; CoefficientList[Series[Sum[(Exp[3 x^k] - 1)/3, {k, 1, nmax}], {x, 0, nmax}], x] Range[0, nmax]! // Rest
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PROG
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(PARI) a(n) = n! * sumdiv(n, d, 3^(d-1)/d!); \\ Michel Marcus, Aug 12 2020
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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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