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Search: id:A002214
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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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+0
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; listen)
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OFFSET
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1,3
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REFERENCES
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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
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T. D. Noe, Table of n, a(n) for n=1..200
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FORMULA
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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
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Sequence in context: A046672 A046866 A000988 this_sequence A100408 A140562 A140550
Adjacent sequences: A002211 A002212 A002213 this_sequence A002215 A002216 A002217
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
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More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), May 02 2004
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