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Search: id:A121860
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| A121860 |
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Sum_{d|n} n!/(d!*(n/d)!). |
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+0
1
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| 1, 2, 2, 8, 2, 122, 2, 1682, 10082, 30242, 2, 7318082, 2, 17297282, 3632428802, 36843206402, 2, 2981705126402, 2, 1690185726028802, 3379030566912002, 28158588057602, 2, 76941821303636889602, 1077167364120207360002
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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a(n) = 2 for prime n. It appears that all a(n) belong to A100195[n] Numbers n such that the denominator of BernoulliB[n] is a record. - Alexander Adamchuk (alex(AT)kolmogorov.com), Sep 09 2006
a(n) = 2 iff n is prime.
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FORMULA
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E.g.f.: Sum_{k>0} (exp(x^k)-1)/k!.
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MATHEMATICA
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f[n_] := Block[{d = Divisors@n}, Plus @@ (n!/(d! (n/d)!))]; Array[f, 25] - Robert G. Wilson v Sep 11 2006
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CROSSREFS
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Cf. A057625, A100195.
Adjacent sequences: A121857 A121858 A121859 this_sequence A121861 A121862 A121863
Sequence in context: A086328 A095997 A056189 this_sequence A021442 A143440 A093731
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KEYWORD
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easy,nonn
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AUTHOR
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Vladeta Jovovic (vladeta(AT)Eunet.yu), Sep 09 2006
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EXTENSIONS
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More terms from Robert G. Wilson v Sep 11 2006
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