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A060092
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Triangle T(n,k) of k-block ordered bicoverings of an unlabeled n-set.
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2
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3, 7, 16, 12, 63, 125, 90, 18, 162, 722, 1716, 1680, 25, 341, 2565, 11350, 27342, 29960, 7560, 33, 636, 7180, 49860, 208302, 503000, 631512, 302400, 42, 1092, 17335, 173745, 1099602, 4389875, 10762299, 14975730, 9632700, 1247400
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,1
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FORMULA
| E.g.f. for k-block ordered bicoverings of an unlabeled n-set is exp(-x-x^2/2*y/(1-y))*Sum_{k=0..inf} 1/(1-y)^binomial(k, 2)*x^k/k!.
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EXAMPLE
| [3], [7, 16], [12, 63, 125, 90], [18, 162, 722, 1716, 1680], [25, 341, 2565, 11350, 27342, 29960, 7560], [33, 636, 7180, 49860, 208302, 503000, 631512, 302400], [42, 1092, 17335, 173745, 1099602, 4389875, 10762299, 14975730, 9632700, 1247400], ...; There are 23=7+16 ordered bicoverings of an unlabeled 3-set: 7 3-block bicoverings and 16 4-block bicoverings, cf. A060090.
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CROSSREFS
| Cf. (row sums) A060090, A060091, A060093-A060095, A060069, A060070, A060051-A060053, A002718, A059443, A003462, A059945-A059951.
Sequence in context: A180503 A153578 A018852 * A035283 A184863 A162159
Adjacent sequences: A060089 A060090 A060091 * A060093 A060094 A060095
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KEYWORD
| nonn
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AUTHOR
| Vladeta Jovovic (vladeta(AT)eunet.rs), Feb 26 2001
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