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A227266
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Number of n X 3 0,1 arrays indicating 2 X 2 subblocks of some larger (n+1) X 4 binary array having a sum of three or less, with rows and columns of the latter in lexicographically nondecreasing order.
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1
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4, 16, 49, 132, 341, 836, 1934, 4232, 8804, 17501, 33392, 61393, 109141, 188181, 315546, 515823, 823812, 1287900, 1974288, 2972226, 4400429, 6414866, 9218134, 13070650, 18303916, 25336135, 34690480, 47016343, 63113917, 83962491
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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) = (1/362880)*n^9 + (1/40320)*n^8 + (5/12096)*n^7 + (19/2880)*n^6 - (611/17280)*n^5 + (3407/5760)*n^4 - (5281/9072)*n^3 - (66509/10080)*n^2 + (22991/504)*n - 59 for n>3.
G.f.: x*(4 - 24*x + 69*x^2 - 118*x^3 + 146*x^4 - 162*x^5 + 177*x^6 - 156*x^7 + 90*x^8 - 31*x^9 + 9*x^10 - 4*x^11 + x^12) / (1 - x)^10.
a(n) = 10*a(n-1) - 45*a(n-2) + 120*a(n-3) - 210*a(n-4) + 252*a(n-5) - 210*a(n-6) + 120*a(n-7) - 45*a(n-8) + 10*a(n-9) - a(n-10) for n>13.
(End)
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EXAMPLE
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Some solutions for n=4:
..1..1..1....1..1..0....1..1..1....1..1..1....1..1..1....1..1..1....1..1..1
..1..1..0....1..1..0....1..1..1....0..0..1....1..0..0....1..0..0....1..1..0
..1..0..0....1..0..0....1..0..1....0..0..1....1..0..0....1..0..0....1..1..0
..1..0..0....1..0..0....1..0..0....0..0..0....1..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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