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A250808
Number of (n+1) X (4+1) 0..2 arrays with nondecreasing x(i,j)-x(i,j-1) in the i direction and nondecreasing min(x(i,j),x(i-1,j)) in the j direction.
1
441, 1731, 6171, 20631, 66291, 207831, 641571, 1961031, 5955891, 18013431, 54331971, 163579431, 491905491, 1478051031, 4438822371, 13325805831, 39996095091, 120025640631, 360151632771, 1080604320231, 3242111804691
OFFSET
1,1
LINKS
FORMULA
Empirical: a(n) = 6*a(n-1) - 11*a(n-2) + 6*a(n-3); a(n) = (620*3^n - 570*2^n + 162)/2.
Empirical g.f.: 3*x*(147 - 305*x + 212*x^2) / ((1 - x)*(1 - 2*x)*(1 - 3*x)). - Colin Barker, Nov 20 2018
EXAMPLE
Some solutions for n=4:
..2..2..2..1..2....2..1..0..0..0....1..1..1..1..1....1..1..1..1..1
..0..0..0..0..1....0..0..0..1..1....0..0..0..0..0....1..1..1..1..1
..0..0..0..0..1....0..0..0..1..1....1..1..1..1..2....0..0..0..1..1
..0..0..1..1..2....1..1..1..2..2....0..0..0..0..1....0..0..0..1..1
..0..0..1..1..2....0..0..0..2..2....0..1..1..1..2....0..0..0..1..1
CROSSREFS
Column 4 of A250812.
Sequence in context: A057949 A057950 A343827 * A202400 A014793 A264305
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 27 2014
STATUS
approved