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 A002215 Number of polyhexes with n hexagons, having reflectional symmetry (see Harary and Read for precise definition). (Formerly M0772 N0295) 4
 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; refs; listen; history; text; internal format)
 OFFSET 1,3 REFERENCES 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). LINKS T. D. Noe, Table of n, a(n) for n=1..200 J. Brunvoll, S. J. Cyvin and B. N. Cyvin, Isomer enumeration of polygonal systems..., J. Molec. Struct. (Theochem), 364 (1996), 1-13, Table 10. F. Harary and R. C. Read, The enumeration of tree-like polyhexes, Proc. Edinburgh Math. Soc. (2) 17 (1970), 1-13. FORMULA 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, Mar 14 2004 CROSSREFS Cf. A002212. Sequence in context: A006606 A120421 A005418 * A007562 A222855 A171682 Adjacent sequences:  A002212 A002213 A002214 * A002216 A002217 A002218 KEYWORD nonn AUTHOR EXTENSIONS More terms from Emeric Deutsch, Mar 14 2004 STATUS approved

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Last modified October 23 03:21 EDT 2019. Contains 328335 sequences. (Running on oeis4.)