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A003409
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3C(2n-1,n).
(Formerly M2814)
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4
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3, 9, 30, 105, 378, 1386, 5148, 19305, 72930, 277134, 1058148, 4056234, 15600900, 60174900, 232676280, 901620585, 3500409330, 13612702950, 53017895700, 206769793230, 807386811660, 3156148445580, 12350146091400, 48371405524650
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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REFERENCES
| C. Domb and A. J. Barrett, Enumeration of ladder graphs, Discrete Math. 9 (1974), 341-358.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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CROSSREFS
| Equals 3 * A001700.
Sequence in context: A145268 A148956 * A029651 A148957 A148958 A024332
Adjacent sequences: A003406 A003407 A003408 * A003410 A003411 A003412
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| More terms from Jon E. Schoenfield (jonscho(AT)hiwaay.net), Mar 26 2010
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