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A005396 Number of 2n-step polygons on honeycomb.
(Formerly M4043)
0
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.

Sequence in context: A028849 A287470 A138704 * A056462 A249869 A209446

Adjacent sequences:  A005393 A005394 A005395 * A005397 A005398 A005399

KEYWORD

nonn,changed

AUTHOR

N. J. A. Sloane.

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 August 13 00:27 EDT 2020. Contains 336441 sequences. (Running on oeis4.)