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A194486
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Number of ways to arrange 2 nonattacking knights on the lower triangle of an n X n board
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1
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0, 3, 13, 37, 87, 178, 328, 558, 892, 1357, 1983, 2803, 3853, 5172, 6802, 8788, 11178, 14023, 17377, 21297, 25843, 31078, 37068, 43882, 51592, 60273, 70003, 80863, 92937, 106312, 121078, 137328, 155158, 174667, 195957, 219133, 244303, 271578, 301072
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = (1/8)*n^4 + (1/4)*n^3 - (17/8)*n^2 + (31/4)*n - 8 for n>1.
Empirical g.f.: x^2*(3 - 2*x + 2*x^2 + 2*x^3 - 2*x^4) / (1 - x)^5. - Colin Barker, May 05 2018
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EXAMPLE
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Some solutions for 3 X 3:
..0......0......1......1......0......0......0......1......0......1......0
..0.1....0.0....0.0....0.1....0.1....1.0....1.1....1.0....0.0....0.0....0.0
..0.0.1..1.1.0..0.0.1..0.0.0..1.0.0..1.0.0..0.0.0..0.0.0..0.1.1..1.0.0..1.0.1
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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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