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A066863 Number of binary arrangements without adjacent 1's on n X n staggered hexagonal grid. 3
2, 6, 43, 557, 14432, 719469, 70372090, 13351521479, 4941545691252, 3559349503024593, 4993739972681894885, 13642580224488264353504 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

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..12.

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

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

Eric Weisstein's World of Mathematics, Hard Hexagon Entropy Constant

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]`?(j<=N-2)|false)

+($[i-1][j-1]`?((i>0)*(j>0)*((j mod 2)=0))|false)

+($[i-1][j+1]`?((i>0)*(j<=N-2)*((j mod 2)=0))|false)

+($[i-1][j]`?(i>0)|false)))) end

CROSSREFS

Cf. A006506 A027683 A066864-A066866.

Sequence in context: A198076 A330675 A183313 * A296828 A135815 A055564

Adjacent sequences:  A066860 A066861 A066862 * A066864 A066865 A066866

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jan 25, 2002

STATUS

approved

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Last modified April 7 12:07 EDT 2020. Contains 333305 sequences. (Running on oeis4.)