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Search: id:A130813
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| A130813 |
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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 7-subsets of X containing none of X_i, (i=1,...n). |
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| 128, 1024, 4608, 15360, 42240, 101376, 219648, 439296, 823680, 1464320, 2489344, 4073472, 6449664, 9922560, 14883840, 21829632, 31380096, 44301312, 61529600, 84198400, 113667840, 151557120, 199779840, 260582400, 336585600, 430829568
(list; graph; listen)
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OFFSET
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7,1
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COMMENT
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Number of n permutations (n>=7)of 3 objects u,v,z, with repetition allowed, containing n-7 u's. Example: if n=7 then n-7 =(0) zero u, a(1)=128. [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,7)+binomial(n,2)*binomial(2*n-4,3)-n*binomial(2*n-2,5)-(2*n-6)*binomial(n,3)
a(n)=C(n,n-7)*2^7, n>=7. - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Dec 07 2007
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MAPLE
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a:=n->binomial(2*n, 7)+binomial(n, 2)*binomial(2*n-4, 3)-n*binomial(2*n-2, 5)-(2*n-6)*binomial(n, 3);
seq(binomial(n, n-7)*2^7, n=7..32); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Dec 07 2007
(Maple) seq(binomial(n+6, 7)*2^7, 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, A130811, A130812 [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Aug 05 2008]
Sequence in context: A135271 A123293 A143708 this_sequence A100628 A134630 A133061
Adjacent sequences: A130810 A130811 A130812 this_sequence A130814 A130815 A130816
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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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