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A002214
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Number of unrooted hexagonal polyominoes with n cells and no reflections allowed.
(Formerly M1750 N0694)
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2
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1, 1, 2, 7, 18, 64, 226, 856, 3306, 13249, 53794, 222717, 933438, 3960487, 16970362, 73381453, 319817670, 1403875491, 6202064928, 27559699507, 123115236582, 552654175124, 2491870281372, 11281732737898, 51270697159708
(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)+(1/2)(3x-1)U(x)^2+(1/2)(1+x)U(x^2)+(1/3)xU(x)^3+(2/3)xU(x^3), where U(x)=[1-3x-sqrt(1-6x+5x^2)]/(2x). - Emeric Deutsch (deutsch(AT)duke.poly.edu), May 02 2004
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CROSSREFS
| Sequence in context: A046866 A176813 A000988 * A100408 A103034 A038952
Adjacent sequences: A002211 A002212 A002213 * A002215 A002216 A002217
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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 Emeric Deutsch (deutsch(AT)duke.poly.edu), May 02 2004
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