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A046996
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Number of Baxter permutations: A001181/2.
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2
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1, 3, 11, 46, 211, 1037, 5377, 29101, 163120, 941480, 5570280, 33664996, 207249719, 1296670793, 8229378293, 52895993341, 343891293422, 2258771535962, 14974619271658, 100117092310368, 674548712552456
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,2
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MATHEMATICA
| Sum[Binomial[n+1, k-1] Binomial[n+1, k] Binomial[n+1, k+1], {k, 1, n}]/(2 Binomial[n+1, 1] Binomial[n+1, 2])
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CROSSREFS
| Sequence in context: A006605 A193074 A086521 * A129579 A030814 A030976
Adjacent sequences: A046993 A046994 A046995 * A046997 A046998 A046999
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KEYWORD
| nonn,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| More terms from Olivier Gerard (olivier.gerard(AT)gmail.com), Jun 26 2001
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