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A208009
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Number of n X 4 0..1 arrays avoiding 0 0 0 and 1 0 1 horizontally and 0 0 1 and 0 1 1 vertically.
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1
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9, 81, 261, 841, 1943, 4489, 8643, 16641, 28509, 48841, 77129, 121801, 181131, 269361, 382503, 543169, 743633, 1018081, 1353069, 1798281, 2331999, 3024121, 3841451, 4879681, 6090213, 7601049, 9343473, 11485321, 13932179, 16900321
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 2*a(n-1) + 4*a(n-2) - 10*a(n-3) - 5*a(n-4) + 20*a(n-5) - 20*a(n-7) + 5*a(n-8) + 10*a(n-9) - 4*a(n-10) - 2*a(n-11) + a(n-12).
Empirical g.f.: x*(9 + 63*x + 63*x^2 + 85*x^3 + 72*x^4 + 74*x^5 - 12*x^6 - 6*x^7 + 15*x^8 - x^9 - 3*x^10 + x^11) / ((1 - x)^7*(1 + x)^5). - Colin Barker, Jun 26 2018
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EXAMPLE
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Some solutions for n=4:
..1..0..0..1....1..1..0..0....0..1..0..0....1..0..0..1....0..1..0..0
..1..0..0..1....0..0..1..0....0..1..0..0....0..1..1..0....1..1..1..0
..1..0..0..1....0..1..0..0....0..1..0..0....1..0..0..1....0..1..0..0
..1..0..0..1....0..0..1..0....0..1..0..0....0..1..1..0....0..0..1..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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