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A234259
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Number of (n+1) X (1+1) 0..2 arrays with every 2 X 2 subblock having its diagonal sum differing from its antidiagonal sum by 2 (constant-stress 1 X 1 tilings).
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1
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20, 46, 104, 244, 560, 1336, 3104, 7504, 17600, 42976, 101504, 249664, 592640, 1465216, 3490304, 8660224, 20679680, 51437056, 123029504, 306525184, 733982720, 1830762496, 4387119104, 10951020544, 26255605760, 65571905536, 157265199104
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OFFSET
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1,1
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LINKS
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FORMULA
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Empirical: a(n) = 2*a(n-1) + 6*a(n-2) - 12*a(n-3).
G.f.: 2*x*(10 + 3*x - 54*x^2) / ((1 - 2*x)*(1 - 6*x^2)).
a(n) = 2^(2+n) + 2^((-3+n)/2)*3^((-1+n)/2)*(12-12*(-1)^n+5*sqrt(6)+5*(-1)^n*sqrt(6)).
(End)
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EXAMPLE
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Some solutions for n=5:
0 2 0 0 0 2 2 0 0 0 2 0 0 2 2 0 0 2 0 2
2 2 2 0 1 1 2 2 0 2 2 2 0 0 2 2 2 2 2 2
0 2 2 2 2 0 0 2 0 0 2 0 2 0 2 0 2 0 2 0
0 0 0 2 0 0 2 2 0 2 2 2 1 1 1 1 2 2 1 1
2 0 1 1 2 0 0 2 2 2 0 2 2 0 2 0 0 2 2 0
2 2 0 2 0 0 2 2 2 0 1 1 1 1 1 1 1 1 0 0
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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