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Search: id:A002215
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| A002215 |
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Number of polyhexes with n hexagons, having reflectional symmetry (see Harary and Read for precise definition).
(Formerly M0772 N0295)
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+0
3
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| 1, 1, 2, 3, 6, 10, 20, 36, 72, 137, 274, 543, 1086, 2219, 4438, 9285, 18570, 39587, 79174, 171369, 342738, 751236, 1502472, 3328218, 6656436, 14878455, 29756910, 67030785, 134061570, 304036170, 608072340, 1387247580, 2774495160
(list; graph; listen)
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OFFSET
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1,3
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REFERENCES
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J. Brunvoll, S. J. Cyvin and B. N. Cyvin, Isomer enumeration of polygonal systems..., J. Molec. Struct. (Theochem), 364 (1996), 1-13. (See Table 10.)
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. = z+(1+2z)U(z^2) where U(z)=[1-3z-sqrt(1-6z+5z^2)]/(2z) (eq. (16) in the Harary-Read paper). a(2n)=A002212(n), n>=1; a(2n+1)=2*A002212(n), n>=1. - Emeric Deutsch (deutsch(AT)duke.poly.edu), Mar 14 2004
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CROSSREFS
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Cf. A002212.
Sequence in context: A006606 A120421 A005418 this_sequence A007562 A008929 A066062
Adjacent sequences: A002212 A002213 A002214 this_sequence A002216 A002217 A002218
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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), Mar 14 2004
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