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Search: id:A130811
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| A130811 |
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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 5-subsets of X containing none of X_i, (i=1,...n). |
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3
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| 32, 192, 672, 1792, 4032, 8064, 14784, 25344, 41184, 64064, 96096, 139776, 198016, 274176, 372096, 496128, 651168, 842688, 1076768, 1360128, 1700160, 2104960, 2583360, 3144960, 3800160, 4560192, 5437152, 6444032, 7594752, 8904192
(list; graph; listen)
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OFFSET
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5,1
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COMMENT
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Number of n permutations (n>=5)of 3 objects u,v,z, with repetition allowed, containing n-5 u's. Example: if n=5 then n-5 =(0) zero u, a(1)=32. [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Aug 05 2008]
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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,5)+(2*n-4)*binomial(n,2)-n*binomial(2*n-2,3)
a(n)=C(n,n-5)*2^5,n>=5. - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Dec 07 2007
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MAPLE
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a:=n->binomial(2*n, 5)+(2*n-4)*binomial(n, 2)-n*binomial(2*n-2, 3)
seq(binomial(n, n-5)*2^5, n=5..34); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Dec 07 2007
(Maple) seq(binomial(n+4, 5)*2^5, n=1..22); [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Aug 05 2008]
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CROSSREFS
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A038207, A000079, A001787, A001788, A001789, A003472, A054849, A002409, A054851, A140325, A140354, A046092, A130809, A130810 [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Aug 05 2008]
Adjacent sequences: A130808 A130809 A130810 this_sequence A130812 A130813 A130814
Sequence in context: A029534 A120046 A019560 this_sequence A119286 A125342 A126500
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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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