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Search: id:A060094
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| A060094 |
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Number of 6-block ordered bicoverings of an unlabeled n-set. |
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+0
3
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| 0, 0, 0, 0, 90, 1716, 11350, 49860, 173745, 519345, 1389078, 3411060, 7821950, 16949910, 35013240, 69404416, 132703770, 245767890, 442372300, 776064960, 1330117230, 2231754820, 3672227850, 5934754020, 9432962515, 14763202395
(list; graph; listen)
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OFFSET
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0,5
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LINKS
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Harry J. Smith, Table of n, a(n) for n=0,...,1000
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FORMULA
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a(n) = binomial(n + 14, n) - 6*binomial(n + 9, 9) - 15*binomial(n + 6, 6) + 30*binomial(n + 5, 5) + 60*binomial(n + 3, 3) - 50*binomial(n + 2, 2) - 180*binomial(n + 1, 1) + 240*binomial(n, 0) - 80*binomial(n - 1, - 1); G.f.: - y^4*(366*y - 16950*y^8 + 36420*y^7 - 54120*y^6 + 56290*y^5 - 40335*y^4 + 18840*y^3 - 4940*y^2 - 960*y^10 + 80*y^11 + 5220*y^9 + 90)/( - 1 + y)^15; 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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PROGRAM
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(PARI) { for (n=0, 1000, a=binomial(n + 14, n) - 6*binomial(n + 9, 9) - 15*binomial(n + 6, 6) + 30*binomial(n + 5, 5) + 60*binomial(n + 3, 3) - 50*binomial(n + 2, 2) - 180*binomial(n + 1, 1) + 240*binomial(n, 0) - 80*binomial(n - 1, - 1); if (n==0, a=0); write("b060094.txt", n, " ", a); ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Jul 01 2009]
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CROSSREFS
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Cf. A060090-A060093, A060095, A060069, A060070, A060051-A060053, A002718, A059443, A003462, A059945-A059951.
Sequence in context: A166817 A166799 A001561 this_sequence A065951 A008393 A055603
Adjacent sequences: A060091 A060092 A060093 this_sequence A060095 A060096 A060097
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KEYWORD
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nonn
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AUTHOR
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Vladeta Jovovic (vladeta(AT)eunet.rs), Feb 26 2001
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