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Search: id:A121316
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| A121316 |
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Unlabeled version of A055203: number of different relations between n intervals (of nonzero length) on a line, up to permutation of intervals. |
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+0
2
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| 1, 1, 7, 75, 1105, 20821, 478439, 12977815, 405909913, 14382249193, 569377926495
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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Also number of labeled multigraphs without isolated vertices and with n edges.
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FORMULA
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a(n) = (1/n!)* Sum_{k=0..n} |Stirling1(n,k)|*A055203(k). a(n) = Sum_{k>=0} binomial(k*(k-1)/2+n-1,n)/2^(k+1).
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MAPLE
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seq(value(Sum(binomial(k*(k-1)/2+n-1, n)/2^(k+1), k=0..infinity)), n=0..20);
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CROSSREFS
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Cf. A121251, A104209.
Sequence in context: A106162 A157706 A127190 this_sequence A066302 A139472 A114470
Adjacent sequences: A121313 A121314 A121315 this_sequence A121317 A121318 A121319
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KEYWORD
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nonn
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AUTHOR
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Goran Kilibarda and Vladeta Jovovic (vladeta(AT)eunet.rs), Aug 25 2006
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