A046170 Number of self-avoiding walks on a 2-D lattice of length n which start at the origin, take first step in the {+1,0} direction and whose vertices are always nonnegative in x and y.

1, 2, 5, 12, 30, 73, 183, 456, 1151, 2900, 7361, 18684, 47652, 121584, 311259, 797311, 2047384, 5260692, 13542718, 34884239, 89991344, 232282110, 600281932, 1552096361, 4017128206, 10401997092, 26957667445, 69892976538