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A007946
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6*(2*n+1)! / ((n!)^2*(n+3)).
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3
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2, 9, 36, 140, 540, 2079, 8008, 30888, 119340, 461890, 1790712, 6953544, 27041560, 105306075, 410605200, 1602881040, 6263890380, 24502865310, 95937144600, 375945078600, 1474358525640, 5786272150230, 22724268808176
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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COMMENTS
| If Y is a fixed 2-subset of a 2n-set X then a(n-2) is the number of (n-1)-subsets of X intersecting Y. - Milan R. Janjic (agnus(AT)blic.net), Oct 21 2007
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LINKS
| Milan Janjic, Two Enumerative Functions
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FORMULA
| a(n)=binom(2n+2, n)+binom(2n+3, n) - Emeric Deutsch (deutsch(AT)duke.poly.edu), May 16 2003
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CROSSREFS
| Sequence in context: A192702 A073989 A134759 * A135593 A027995 A077836
Adjacent sequences: A007943 A007944 A007945 * A007947 A007948 A007949
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KEYWORD
| nonn
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AUTHOR
| David W. Wilson (davidwwilson(AT)comcast.net) and Dean Hickerson (dean.hickerson(AT)yahoo.com), Apr 21 1997
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