A066866 Number of binary arrangements without adjacent 1's in n X n rhombic hexagonal grid torus.

1, 5, 22, 201, 4216, 162314, 12329633, 1831137521, 528106112383, 296848246952000, 324932515409958655, 692572885398506075946, 2874785146216927021053015, 23237716875160177498526082523, 365789982527236500400197753931927, 11212996751916827855636781928754023265

Offset: 1

Author

R. H. Hardin, Jan 25 2002

Keywords

• nonn
• hard

Examples

			neighbors for n=4:
.|/ |/ |/ |/
-o--o--o--o-
/| /| /| /|
.|/ |/ |/ |/
-o--o--o--o-
/| /| /| /|
.|/ |/ |/ |/
-o--o--o--o-
/| /| /| /|
.|/ |/ |/ |/
-o--o--o--o-
/| /| /| /|
		

References

• Steven R. Finch, Mathematical Constants, Cambridge, 2003, pp. 342-349.
• J. Katzenelson and R. P. Kurshan, S/R: A Language for Specifying Protocols and Other Coordinating Processes, pp. 286-292 in Proc. IEEE Conf. Comput. Comm., 1986.

Links

• Sean A. Irvine, Table of n, a(n) for n = 1..18
• Steven R. Finch, Hard Square Entropy Constant [Broken link]
• Steven R. Finch, Hard Square Entropy Constant [From the Wayback machine]
• Sean A. Irvine, Java program (github)
• V. Kotesovec, Non-attacking chess pieces, 6ed, 2013, p. 73.

Crossrefs

Cf. A006506, A027683, A066863, A066864, A066865.

Extensions

Terms a(11)-a(12) from Vaclav Kotesovec, May 07 2012

a(13) from Vaclav Kotesovec, Aug 15 2016

a(14) from Vaclav Kotesovec, May 24 2021

a(15)-a(16) from Sean A. Irvine, Nov 18 2023