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A002213
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Number of polyhexes rooted at a hexagon and containing n hexagons.
(Formerly M3907 N1603)
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2
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1, 1, 5, 20, 84, 354, 1540, 6704, 29610, 131745, 591049, 2669346, 12131148, 55431285, 254539897, 1174027598, 5436826110, 25269402555, 117838870833, 551192276450, 2585418254532, 12158383558066, 57313008207960
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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REFERENCES
| F. Harary and R. C. Read, The enumeration of tree-like polyhexes, Proc. Edinb. Math. Soc. (2) 17 (1970), 1-13.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
| T. D. Noe, Table of n, a(n) for n=1..200
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FORMULA
| G.f.: x+xU(x)+(3/2)xU(x)^2+(1/2)xU(x^2)+(1/3)xU(x)^3+(2/3)xU(x^3), where U(x)=[1-3x-sqrt((1-x)(1-5x))]/(2x).
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CROSSREFS
| Sequence in context: A183933 A056884 A006749 * A099949 A006231 A069007
Adjacent sequences: A002210 A002211 A002212 * A002214 A002215 A002216
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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
| Edited by Emeric Deutsch (deutsch(AT)duke.poly.edu), Feb 18 2004
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