A175895 Number of lattice paths from (0,0) to (n,n) using steps S={(k,0),(0,k),(1,1)|0<k<=2} which never go above the line y=x.

1, 2, 9, 50, 314, 2116, 14949, 109246, 818978, 6263072, 48668366, 383182648, 3050196328, 24506969724, 198482172753, 1618700191002, 13281652367078, 109564878995724, 908171084052990, 7560049450347964, 63176859344766204

Offset

0,2

Links

Table of n, a(n) for n=0..20.

Example

a(2)=9 because we can reach (2,2) in the following ways:
(1,0),(1,0),(0,1),(0,1)
(1,0),(1,0),(0,2)
(2,0),(0,1),(0,1)
(2,0),(0,2)
(1,0),(1,1),(0,1)
(1,0),(0,1),(1,1)
(1,1),(1,0),(0,1)
(1,1),(0,1),(1,0)
(1,1)(1,1)

Crossrefs

Cf. A006318

Sequence in context: A211789 A192945 A271960 * A020087 A277378 A026945

Adjacent sequences: A175892 A175893 A175894 * A175896 A175897 A175898

Keyword

nonn

Author

Eric Werley, Dec 05 2010

Status

approved