256365292443domain: NAppears in sequencesNumber of paths of length n in the first quadrant, starting at the origin and consisting of 2 kinds of upsteps U=(1,1) (U1 and U2), 3 kinds of flatsteps F=(1,0) (F1, F2 and F3) and 1 kind of downsteps D=(1,-1).at n=15A134425