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A203650
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1/25 the number of (n+1) X 3 0..4 arrays with every 2 X 2 subblock having equal diagonal elements or equal antidiagonal elements.
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1
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81, 1517, 28057, 519445, 9616161, 178019197, 3295578857, 61009378085, 1129435635441, 20908668388877, 387071560403257, 7165659241743925, 132654210800937921, 2455760042384774557, 45462238622967429257
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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) = 17*a(n-1) +28*a(n-2).
G.f.: x*(81 + 140*x) / (1 - 17*x - 28*x^2).
a(n) = (2^(-1-n)*((17-sqrt(401))^n*(-77+5*sqrt(401)) + (17+sqrt(401))^n*(77+5*sqrt(401))))/sqrt(401).
(End)
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EXAMPLE
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Some solutions for n=4:
..3..1..2....3..4..3....2..2..1....0..3..2....2..0..1....4..4..4....1..2..4
..4..3..1....1..3..2....3..2..2....3..4..3....4..2..0....2..4..4....3..1..2
..2..4..3....2..1..3....1..3..2....3..3..3....1..4..2....1..2..4....0..3..1
..2..2..4....3..2..1....0..1..3....4..3..4....0..1..4....1..1..2....2..0..3
..1..2..2....2..4..2....4..0..1....4..4..1....1..3..1....0..1..1....0..4..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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