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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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4
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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;
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listen;
history;
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OFFSET
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1,3
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REFERENCES
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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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FORMULA
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G.f.: z + (1+2*z)*U(z^2) where U(z) = (1 - 3*z - sqrt(1-6*z+5*z^2))/(2*z) (eq. (16) in the Harary-Read paper).
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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