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A229449
Number of 6 X n 0..2 arrays with horizontal differences mod 3 never 1, vertical differences mod 3 never -1, and rows and columns lexicographically nondecreasing.
1
23, 84, 293, 915, 2546, 6374, 14536, 30571, 59969, 110816, 194535, 326723, 528084, 825458, 1252946, 1853131, 2678395, 3792332, 5271257, 7205811, 9702662, 12886302, 16900940, 21912491, 28110661, 35711128, 44957819, 56125283, 69521160, 85488746
OFFSET
1,1
LINKS
FORMULA
Empirical: a(n) = (2/15)*n^6 - (5/8)*n^5 + (9/2)*n^4 - (55/8)*n^3 + (283/15)*n^2 - 4*n + 11.
Conjectures from Colin Barker, Sep 17 2018: (Start)
G.f.: x*(23 - 77*x + 188*x^2 - 177*x^3 + 159*x^4 - 31*x^5 + 11*x^6) / (1 - x)^7.
a(n) = 7*a(n-1) - 21*a(n-2) + 35*a(n-3) - 35*a(n-4) + 21*a(n-5) - 7*a(n-6) + a(n-7) for n>7.
(End)
EXAMPLE
Some solutions for n=4.
..0..0..0..0....0..2..2..2....0..2..2..2....0..2..2..2....0..2..2..2
..0..0..0..0....1..0..2..2....0..2..2..2....1..0..2..2....1..0..2..2
..0..0..0..0....2..1..0..0....0..2..2..2....1..1..0..2....1..1..0..2
..1..1..1..1....2..1..0..0....1..0..2..2....2..1..0..0....1..1..1..0
..2..2..2..2....2..2..1..1....1..0..2..2....2..1..0..0....2..1..1..0
..2..2..2..2....2..2..2..2....1..1..0..0....2..1..0..0....2..1..1..1
CROSSREFS
Row 6 of A229445.
Sequence in context: A262119 A104068 A304839 * A060456 A056580 A010011
KEYWORD
nonn
AUTHOR
R. H. Hardin, Sep 23 2013
STATUS
approved