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Search: id:A073090
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| A073090 |
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Number of permutations p from (1,2,3,...,n) to (1,2,3...,n) such that 1/p(1)+2/p(2)+...+n/p(n) is an integer. |
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+0
1
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| 1, 1, 1, 2, 2, 8, 8, 22, 104, 1128, 1128, 14520, 14520
(list; graph; listen)
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OFFSET
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1,4
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EXAMPLE
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p(1,2)=(1,2) is the only permutation such that 1/p(1)+2/p(2) is an integer hence a(2)=1
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PROGRAM
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(PARI) a(n)=if(n<0, 0, sum(k=1, n!, if(frac(sum(i=1, n, i/component(numtoperm(n, k), i))), 0, 1)))
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CROSSREFS
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Sequence in context: A082887 A137583 A099328 this_sequence A120544 A155950 A162959
Adjacent sequences: A073087 A073088 A073089 this_sequence A073091 A073092 A073093
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KEYWORD
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more,nonn
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AUTHOR
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Benoit Cloitre (benoit7848c(AT)orange.fr), Aug 18 2002
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EXTENSIONS
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More terms from John W. Layman (layman(AT)math.vt.edu), Feb 06 2004
Corrected by Benoit Cloitre (benoit7848c(AT)orange.fr), Feb 21, 2004
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