OFFSET
0
COMMENTS
The Motzkin step set is U=(1,1), H=(1,0) and D=(1,-1). An excursion is a path starting at (0,0), ending on the x-axis and never crossing the x-axis, i.e., staying at nonnegative altitude.
LINKS
FORMULA
G.f.: 1+t+t^3.
EXAMPLE
The only excursions of this type are the empty walk, H and UHD.
CROSSREFS
KEYWORD
nonn,walk
AUTHOR
Valerie Roitner, Nov 25 2019
STATUS
approved