A006774 Number of 2n-step polygons on honeycomb.

1, 0, 0, 1, 0, 3, 2, 12, 18, 65, 138, 432, 1074, 3231, 8718, 25999, 73650, 220215, 643546, 1937877, 5783700, 17564727, 53222094, 163009086, 499634508, 1542392088, 4770925446, 14832934031, 46227584010, 144632622552, 453628244950

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn

References

• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• I. Jensen, Table of n, a(n) for n = 0..79
• I. G. Enting and A. J. Guttmann, Polygons on the honeycomb lattice, J. Phys. A 22 (1989), 1371-1384.
• I. Jensen, More terms

Formula

a(n) = A005396(n) / (2*n), n > 1. - Sean A. Irvine, Aug 06 2020

Extensions

a(0)-a(2) inserted by Sean A. Irvine, Aug 06 2020