OFFSET
0,9
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..2500
Wikipedia, Counting lattice paths
EXAMPLE
a(7) = 1: /\
/\/ \/\
/\/ \/\
a(8) = 2: /\ /\
/\/ \ /\ /\ / \/\
/\/ \/ \/\ /\/ \/ \/\
a(9) = 1: /\
/\ / \ /\
/\/ \/ \/ \/\
a(10) = 1: /\
/\/ \/\
/\/ \/\
/\/ \/\ .
MAPLE
b:= proc(x, y, v) option remember; (t-> `if`(x=t, 1,
`if`(x<t, 0, add(b(x-1-2*i, y-1, 0), i=1..y-1)+
`if`(v=1, add(b(x-1-2*i, y+1, v), i=1..y), 0))))(3*y-2)
end:
a:= n-> `if`(n=0, 1, b(2*n-1, 1$2)):
seq(a(n), n=0..50);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Apr 12 2024
STATUS
approved