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A219515
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Number of n X 4 arrays of the minimum value of corresponding elements and their horizontal, diagonal or antidiagonal neighbors in a random, but sorted with lexicographically nondecreasing rows and columns, 0..1 n X 4 array.
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1
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4, 5, 24, 68, 187, 465, 1090, 2430, 5181, 10575, 20714, 39046, 71023, 124990, 213360, 354136, 572847, 904971, 1398924, 2119700, 3153253, 4611718, 6639574, 9420858, 13187545, 18229215, 24904134, 33651882, 45007667, 59618470, 78261172
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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) = (1/6720)*n^8 - (1/360)*n^7 + (41/1440)*n^6 + (7/18)*n^5 - (41099/2880)*n^4 + (68651/360)*n^3 - (6724661/5040)*n^2 + (58709/12)*n - 7380 for n>6.
G.f.: x*(4 - 31*x + 123*x^2 - 304*x^3 + 523*x^4 - 660*x^5 + 655*x^6 - 528*x^7 + 357*x^8 - 217*x^9 + 156*x^10 - 128*x^11 + 74*x^12 - 15*x^13 - 3*x^14) / (1 - x)^9.
a(n) = 9*a(n-1) - 36*a(n-2) + 84*a(n-3) - 126*a(n-4) + 126*a(n-5) - 84*a(n-6) + 36*a(n-7) - 9*a(n-8) + a(n-9) for n>15.
(End)
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EXAMPLE
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Some solutions for n=3:
..0..0..0..0....0..0..0..0....0..0..0..0....0..0..0..1....0..0..0..0
..0..0..0..0....0..0..0..0....0..0..0..0....0..0..0..1....0..0..0..0
..0..0..1..0....1..0..1..1....1..0..1..0....1..1..1..1....0..0..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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