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

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

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