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Search: id:A130812
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| A130812 |
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If X_1,...,X_n is a partition of a 2n-set X into 2-blocks then a(n) is equal to the number of 6-subsets of X containing none of X_i, (i=1,...n). |
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| 64, 448, 1792, 5376, 13440, 29568, 59136, 109824, 192192, 320320, 512512, 792064, 1188096, 1736448, 2480640, 3472896, 4775232, 6460608, 8614144, 11334400, 14734720, 18944640, 24111360, 30401280, 38001600, 47121984, 57996288
(list; graph; listen)
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OFFSET
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6,1
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LINKS
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Milan Janjic, Two Enumerative Functions
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FORMULA
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a(n)=binomial(2*n,6)+binomial(n,2)*binomial(2*n-4,2)-n*binomial(2*n-2,4)-binomial(n,3)
a(n)=C(n,n-6)*2^6,n>=6. - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Dec 07 2007
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MAPLE
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a:=n->binomial(2*n, 6)+binomial(n, 2)*binomial(2*n-4, 2)-n*binomial(2*n-2, 4)-binomial(n, 3);
seq(binomial(n, n-6)*2^6, n=6..32); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Dec 07 2007
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CROSSREFS
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Sequence in context: A105918 A017618 A092211 this_sequence A016803 A066430 A115740
Adjacent sequences: A130809 A130810 A130811 this_sequence A130813 A130814 A130815
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KEYWORD
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nonn
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AUTHOR
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Milan R. Janjic (agnus(AT)blic.net), Jul 16 2007
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