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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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2
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1, 1, 7, 75, 1105, 20821, 478439, 12977815, 405909913, 14382249193, 569377926495, 24908595049347, 1193272108866953, 62128556769033261, 3493232664307133871, 210943871609662171055, 13615857409567572389361, 935523911378273899335537
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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COMMENTS
| Also number of labeled multigraphs without isolated vertices and with n edges.
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LINKS
| Nathaniel Johnston, Table of n, a(n) for n = 0..125
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FORMULA
| 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
| seq(sum(binomial(k*(k-1)/2+n-1, n)/2^(k+1), k=0..infinity), n=0..20);
with(combinat): A121316:=proc(n) return (1/n!)*add(abs(stirling1(n, k))*A055203(k), k=0..n): end: seq(A121316(n), n=0..20); # Nathaniel Johnston, Apr 28 2011
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CROSSREFS
| Cf. A121251, A104209.
Sequence in context: A197763 A202251 A127190 * A066302 A139472 A180356
Adjacent sequences: A121313 A121314 A121315 * A121317 A121318 A121319
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KEYWORD
| nonn
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AUTHOR
| Goran Kilibarda and Vladeta Jovovic (vladeta(AT)eunet.rs), Aug 25 2006
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