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A227554
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Number of n X 2 0,1 arrays indicating 2 X 2 subblocks of some larger (n+1) X 3 binary array having nonzero determinant, with rows and columns of the latter in lexicographically nondecreasing order.
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1
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4, 12, 33, 81, 179, 362, 680, 1201, 2014, 3232, 4995, 7473, 10869, 15422, 21410, 29153, 39016, 51412, 66805, 85713, 108711, 136434, 169580, 208913, 255266, 309544, 372727, 445873, 530121, 626694, 736902, 862145, 1003916, 1163804, 1343497
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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) = (1/40)*n^5 + (17/24)*n^3 + (34/15)*n + 1.
G.f.: x*(4 - 12*x + 21*x^2 - 17*x^3 + 8*x^4 - x^5) / (1 - x)^6.
a(n) = 6*a(n-1) - 15*a(n-2) + 20*a(n-3) - 15*a(n-4) + 6*a(n-5) - a(n-6) for n>6.
(End)
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EXAMPLE
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Some solutions for n=4:
..0..0....0..1....1..1....0..1....0..0....0..1....0..0....0..0....1..0....0..1
..0..0....1..0....1..1....0..0....0..1....0..1....1..1....0..0....0..0....1..0
..1..1....1..0....0..1....1..1....1..1....1..1....1..1....0..0....0..0....0..0
..1..1....0..0....0..0....0..0....1..1....0..0....0..0....1..0....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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