|
|
A250757
|
|
Number of (2+1) X (n+1) 0..2 arrays with nondecreasing x(i,j)-x(i,j-1) in the i direction and nondecreasing x(i,j)+x(i-1,j) in the j direction.
|
|
1
|
|
|
105, 237, 423, 663, 957, 1305, 1707, 2163, 2673, 3237, 3855, 4527, 5253, 6033, 6867, 7755, 8697, 9693, 10743, 11847, 13005, 14217, 15483, 16803, 18177, 19605, 21087, 22623, 24213, 25857, 27555, 29307, 31113, 32973, 34887, 36855, 38877, 40953, 43083
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
LINKS
|
|
|
FORMULA
|
Empirical: a(n) = 27*n^2 + 51*n + 27.
G.f.: 3*x*(35 - 26*x + 9*x^2) / (1 - x)^3.
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n>3.
(End)
|
|
EXAMPLE
|
Some solutions for n=4:
..1..1..1..1..1....2..2..2..2..2....1..2..2..2..2....1..2..2..2..2
..0..1..1..1..1....0..0..1..1..1....0..2..2..2..2....1..2..2..2..2
..0..1..1..1..1....0..0..2..2..2....0..2..2..2..2....0..1..1..2..2
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|