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A066866 Number of binary arrangements without adjacent 1's in n X n rhombic hexagonal grid torus. 12
1, 5, 22, 201, 4216, 162314, 12329633, 1831137521, 528106112383, 296848246952000, 324932515409958655, 692572885398506075946, 2874785146216927021053015 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

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

Table of n, a(n) for n=1..13.

Steven R. Finch, Hard Square Entropy Constant [Broken link]

Steven R. Finch, Hard Square Entropy Constant [From the Wayback machine]

V. Kotesovec, Non-attacking chess pieces, 6ed, 2013, p. 73.

EXAMPLE

neighbors for n=4:

.|/ |/ |/ |/

-o--o--o--o-

/| /| /| /|

.|/ |/ |/ |/

-o--o--o--o-

/| /| /| /|

.|/ |/ |/ |/

-o--o--o--o-

/| /| /| /|

.|/ |/ |/ |/

-o--o--o--o-

/| /| /| /|

PROG

[S/R] proc a

stvar $[N][N]:boolean

init $[][] := false

cyset true

asgn $[][]->{false, true}

kill +[i in 0.. N-1](

+[j in 0.. N-1](

$[i][j]`*(

$[i][(j+1) mod N]`

+$[(i-1) mod N][(j+1) mod N]`

+$[(i-1) mod N][j]` ))) end

CROSSREFS

Cf. A006506 A027683 A066863 A066864 A066865.

Sequence in context: A129437 A048252 A208804 * A115657 A066865 A183902

Adjacent sequences:  A066863 A066864 A066865 * A066867 A066868 A066869

KEYWORD

nonn,hard

AUTHOR

R. H. Hardin, Jan 25 2002

EXTENSIONS

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

a(13) from Vaclav Kotesovec, Aug 15 2016

STATUS

approved

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Last modified March 29 15:16 EDT 2020. Contains 333107 sequences. (Running on oeis4.)