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A191006
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Number of n X n symmetric binary matrices with each 1 adjacent to exactly 1 diagonally neighboring 1
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1
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1, 2, 6, 24, 144, 1296, 16848, 320112, 8963136, 367488576, 22049314560, 1940339681280, 250303818885120, 47307421769287680, 13104155830092687360, 5320287267017631068160, 3165570923875490485555200
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OFFSET
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1,2
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LINKS
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FORMULA
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Empirical: a(n) = a(n-1) * A000930(n+1), so from the formula there
Empirical: a(n) = product(sum(binomial(k+1-2*i,i), i=0..floor((k+1)/3)), k=1..n)
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EXAMPLE
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Some solutions for n=5
..0..0..0..1..0....0..0..0..1..0....1..1..1..1..0....1..0..0..1..0
..0..0..1..0..1....0..0..0..0..1....1..1..1..1..1....0..1..0..1..1
..0..1..1..1..0....0..0..0..1..0....1..1..0..0..0....0..0..0..1..1
..1..0..1..1..0....1..0..1..0..1....1..1..0..1..0....1..1..1..1..1
..0..1..0..0..0....0..1..0..1..0....0..1..0..0..1....0..1..1..1..1
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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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