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A005396 Number of 2n-step polygons on honeycomb.
(Formerly M4043)
1
1, 0, 0, 6, 0, 30, 24, 168, 288, 1170, 2760, 9504, 25776, 84006, 244104, 779970, 2356800, 7487310, 23167656, 73639326, 231348000, 737718534, 2341772136, 7498417956, 23982456384, 77119604400, 248088123192, 800978437674, 2588744704560, 8388692108016, 27217694697000 (list; graph; refs; listen; history; text; internal format)
OFFSET
2,4
REFERENCES
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
M. E. Fisher and M. F. Sykes, Excluded-volume problem and the Ising model of ferromagnetism, Phys. Rev. 114 (1959), 45-58.
FORMULA
a(n) = 2 * n * A006774(n), n > 1. - Sean A. Irvine, Aug 06 2020
CROSSREFS
Cf. A001335.
Sequence in context: A028849 A287470 A138704 * A056462 A249869 A209446
KEYWORD
nonn
AUTHOR
EXTENSIONS
a(11)-a(21) from Sean A. Irvine, Jun 12 2016
a(0)-a(1) inserted and more terms from Sean A. Irvine, Aug 06 2020
STATUS
approved

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Last modified September 8 15:16 EDT 2024. Contains 375753 sequences. (Running on oeis4.)