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 A066863 Number of binary arrangements without adjacent 1's on n X n staggered hexagonal grid. 4
 2, 6, 43, 557, 14432, 719469, 70372090, 13351521479, 4941545691252, 3559349503024593, 4993739972681894885, 13642580224488264353504, 72582736229683196932680697, 751993955499337790653321567382, 15172223086707160824288341875907978 (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..15. 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) 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, A066865, 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 EXTENSIONS More terms from Sean A. Irvine, Nov 15 2023 STATUS approved

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Last modified December 1 13:31 EST 2023. Contains 367475 sequences. (Running on oeis4.)