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Search: id:A028329
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| A028329 |
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Twice central binomial coefficients. |
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+0
5
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| 2, 4, 12, 40, 140, 504, 1848, 6864, 25740, 97240, 369512, 1410864, 5408312, 20801200, 80233200, 310235040, 1202160780, 4667212440, 18150270600, 70690527600, 275693057640, 1076515748880, 4208197927440, 16466861455200
(list; graph; listen)
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OFFSET
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0,1
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COMMENT
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Central elements in the even-Pascal triangle A028326.
If Y is a 3-subset of an 2n-set X then, for n>=3, a(n-1) is the number of (n+1)-subsets of X having at least two elements in common with Y. - Milan R. Janjic (agnus(AT)blic.net), Dec 16 2007
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FORMULA
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G.f.: 2/sqrt(1-4x). a(n)=2*binomial(2n, n).
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MAPLE
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seq(sum(binomial(2*n, n), k=1..2), n=0..23); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Dec 14 2007
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PROGRAM
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(PARI) a(n)=2*binomial(2*n, n)
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CROSSREFS
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a(n)=2*A000984(n).
Bisection of A047073, A063886. First differences of A054113.
Sequence in context: A126946 A113179 A056236 this_sequence A025227 A119430 A074034
Adjacent sequences: A028326 A028327 A028328 this_sequence A028330 A028331 A028332
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KEYWORD
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nonn,easy
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AUTHOR
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Mohammad K. Azarian (ma3(AT)evansville.edu)
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EXTENSIONS
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More terms from James A. Sellers (sellersj(AT)math.psu.edu)
Edited by Michael Somos, Sep 13 2003
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