A099330 Number of Catalan knight paths from (0,0) to (n,2) in the region between and on the lines y=0 and y=3. (See A096587 for the definition of Catalan knight.).

0, 1, 0, 1, 1, 5, 6, 14, 18, 43, 70, 147, 243, 475, 828, 1596, 2852, 5365, 9676, 18037, 32853, 60929, 111394, 205770, 377142, 695519, 1276818, 2351975, 4320935, 7954167, 14620472, 26904824, 49467208, 91010153, 167357080, 307868201

Offset

1,6

Links

Table of n, a(n) for n=1..36.

Formula

Taking A099328 to A099331 as the rows of an array T, the recurrences for these row sequences are given for n>=2 by T(n, 0) = T(n-1, 2) + T(n-2, 1), T(n, 1) = T(n-1, 3) + T(n-2, 0) + T(n-2, 2), T(n, 2) = T(n-1, 0) + T(n-2, 1) + T(n-2, 3), T(n, 3) = T(n-1, 1) + T(n-2, 2), with initial values T(0, 0)=1, T(1, 2)=1.

From Chai Wah Wu, Aug 09 2016: (Start)

a(n) = a(n-1) + a(n-2) - a(n-3) + 3*a(n-4) + a(n-5) + a(n-6) - a(n-7) for n > 7.

G.f.: -x^2*(x^3 - x + 1)/((-x^4 + 2*x^3 + 1)*(x^3 + x^2 + x - 1)). (End)

Example

a(6) counts 6 paths from (0,0) to (6,2); the final move in 1 path is from the point (4,3), the final move in 3 paths is from (4,1) and the final move in the other 2 paths is from (5,0).

Crossrefs

Cf. A099328, A099329, A099331.

Sequence in context: A266304 A359329 A308839 * A322479 A309480 A180686

Adjacent sequences: A099327 A099328 A099329 * A099331 A099332 A099333

Keyword

nonn

Author

Clark Kimberling, Oct 12 2004

Status

approved