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A215785
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Number of permutations of 0..floor((n*7-1)/2) on even squares of an n X 7 array such that each row, column, diagonal and (downwards) antidiagonal of even squares is increasing.
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1
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1, 5, 42, 262, 2465, 15485, 146205, 918637, 8674386, 54503318, 514658321, 3233726365, 30535100957, 191859642509, 1811672635826, 11383190276278, 107488026474001, 675374034791837, 6377352953765373, 40070496565665517
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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) = 61*a(n-2) - 99*a(n-4) - 2*a(n-6).
Empirical g.f.: x*(1 + 5*x - 19*x^2 - 43*x^3 + 2*x^4 - 2*x^5) / (1 - 61*x^2 + 99*x^4 + 2*x^6). - Colin Barker, Jul 23 2018
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EXAMPLE
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Some solutions for n=4:
..0..x..1..x..2..x..3....0..x..1..x..3..x..4....0..x..1..x..2..x..6
..x..4..x..6..x..7..x....x..2..x..5..x..6..x....x..3..x..4..x..8..x
..5..x..8..x..9..x.12....7..x..8..x..9..x.10....5..x..7..x.10..x.12
..x.10..x.11..x.13..x....x.11..x.12..x.13..x....x..9..x.11..x.13..x
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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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