OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..1000
EXAMPLE
a(3)=29 because we can reach (3,3) in the following ways:
by getting to (3,2) in 17 ways and then taking step (0,1), or
by getting to (3,1) in 8 ways and then taking step (0,2), or
by getting to (3,0) in 4 ways and then taking step (0,3).
MAPLE
b:= proc(x, y) option remember; `if`(y>x or y<0, 0,
`if`(x=0, 1, add(b(x-j, y)+b(x, y-j), j=1..3)))
end:
a:= n-> b(n$2):
seq(a(n), n=0..35); # Alois P. Heinz, May 16 2017
MATHEMATICA
b[x_, y_] := b[x, y] = If[y > x || y < 0, 0, If[x == 0, 1, Sum[b[x - j, y] + b[x, y - j], {j, 1, 3}]]];
a[n_] := b[n, n];
a /@ Range[0, 35] (* Jean-François Alcover, Nov 11 2020, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Eric Werley, Dec 05 2010
STATUS
approved