A005396 - OEIS

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A005396

Number of 2n-step polygons on honeycomb.
(Formerly M4043)

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

Table of n, a(n) for n=2..32.

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.