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A066864
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Number of binary arrangements without adjacent 1's on n X n rhombic hexagonal grid.
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18
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1, 2, 6, 42, 524, 13322, 647252, 61758332, 11435477118, 4129523869606, 2902264461628298, 3973109800760143708, 10590895512774862686570, 54979738656662942307796576, 555797909644630436677137498230, 10941698340065066230952215658836402, 419471520990343359533179780148504998680
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OFFSET
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0,2
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COMMENTS
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Also the number of tilings of an (n+1) X (n+1) square using 1 X 1 squares and L-tiles. An L-tile is a 2 X 2 square with the upper right 1 X 1 subsquare removed and no rotations are allowed. a(2) = 6:
._____ _____ _____ _____ _____ _____
|_|_|_| | |_|_| |_|_|_| |_| |_| |_|_|_| |_| |_|
|_|_|_| |___|_| | |_|_| |_|___| |_| |_| | |___|
|_|_|_| |_|_|_| |___|_| |_|_|_| |_|___| |___|_| - Alois P. Heinz, Jun 06 2013
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REFERENCES
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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.
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LINKS
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FORMULA
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Limit_{n->oo} a(n)^(1/n^2) = 1.395485972... (see A085851).
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EXAMPLE
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Neighbors for n=4:
o--o--o--o
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|/ |/ |/ |
o--o--o--o
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|/ |/ |/ |
o--o--o--o
| /| /| /|
|/ |/ |/ |
o--o--o--o
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MAPLE
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a:= proc(n) option remember; local b; b:=
proc(n, l) option remember; local k;
if n<2 then 1
elif min(l[])>0 then b(n-1, map(h->h-1, l))
else for k while l[k]>0 do od; b(n, subsop(k=1, l))+
`if`(n>1 and k<nops(l) and l[k+1]=0,
b(n, subsop(k=2, k+1=1, l)), 0)
fi
end: forget(b);
b(n+1, [0$n+1])
end:
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MATHEMATICA
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$RecursionLimit = 1000; a[n0_] := a[n0] = Module[{b}, b[n_, l_List] := b[n, l] = Module[{k}, Which[n<2, 1, Min[l]>0, b[n-1, l-1], True, For[k = 1, l[[k]] > 0, k++]; b[n, ReplacePart[l, k -> 1]] + If[n>1 && k<Length[l] && l[[k+1]] == 0, b[n, ReplacePart[l, {k -> 2, k+1 -> 1}]], 0]]]; b[n0+1, Array[0&, n0+1]]]; Table[a[n], {n, 0, 15}] (* Jean-François Alcover, Feb 24 2015, after Alois P. Heinz *)
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PROG
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[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)
+($[i-1][j+1]`?((i>0)*(j<=N-2))|false)
+($[i-1][j]`?(i>0)|false) ))) end
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CROSSREFS
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KEYWORD
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nonn,nice,hard
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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