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A060091
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Number of 4-block ordered bicoverings of an unlabeled n-set.
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3
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0, 0, 0, 16, 63, 162, 341, 636, 1092, 1764, 2718, 4032, 5797, 8118, 11115, 14924, 19698, 25608, 32844, 41616, 52155, 64714, 79569, 97020, 117392, 141036, 168330, 199680, 235521, 276318, 322567, 374796, 433566, 499472, 573144, 655248, 746487
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,4
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LINKS
| Harry J. Smith, Table of n, a(n) for n=0,...,1000
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FORMULA
| a(n) = binomial(n + 5, 5) - 4*binomial(n + 2, 2) - 3*binomial(n + 1, 1) + 12*binomial(n, 0) - 6*binomial(n - 1, - 1); G.f.: - y^3*( - 24*y^2 - 16 + 33*y + 6*y^3)/( - 1 + y)^6; E.g.f. for ordered k-block 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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PROG
| (PARI) { for (n=0, 1000, a=binomial(n + 5, 5) - 4*binomial(n + 2, 2) - 3*binomial(n + 1, 1) + 12*binomial(n, 0) - 6*binomial(n - 1, - 1); if (n==0, a=0); write("b060091.txt", n, " ", a); ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Jul 01 2009]
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CROSSREFS
| Cf. A060090, A060092-A060095, A060069, A060070, A060051-A060053, A002718, A059443, A003462, A059945-A059951.
Sequence in context: A022289 A143860 A100176 * A076751 A155985 A090567
Adjacent sequences: A060088 A060089 A060090 * A060092 A060093 A060094
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KEYWORD
| nonn
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AUTHOR
| Vladeta Jovovic (vladeta(AT)eunet.rs), Feb 26 2001
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