A247291 Number of weighted lattice paths B(n) having no uhd strings.

1, 1, 2, 4, 7, 15, 32, 69, 154, 346, 786, 1806, 4180, 9745, 22865, 53938, 127865, 304447, 727733, 1745736, 4201350, 10140975, 24544000, 59551327, 144822097, 352940719, 861839226, 2108381480, 5166749329, 12681855551, 31174671514, 76742344774

Offset: 0

Author

Emeric Deutsch, Sep 16 2014

Keywords

• nonn

Comments

B(n) is the set of lattice paths of weight n that start in (0,0), end on the horizontal axis and never go below this axis, whose steps are of the following four kinds: h = (1,0) of weight 1, H = (1,0) of weight 2, u = (1,1) of weight 2, and d = (1,-1) of weight 1. The weight of a path is the sum of the weights of its steps.

a(n) = A247290(n,0).

Examples

			a(4)=7 because we have hhhh, hhH, hHh, Hhh, HH, hud, and udh.
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..1000
• M. Bona and A. Knopfmacher, On the probability that certain compositions have the same number of parts, Ann. Comb., 14 (2010), 291-306.

Crossrefs

Cf. A247290, A247293, A247295.

Programs

Maple

eq := G = 1+z*G+z^2*G+z^3*(G-z)*G: G := RootOf(eq, G): Gser := series(G, z = 0, 37): seq(coeff(Gser, z, n), n = 0 .. 35);
# second Maple program:
b:= proc(n, y, t) option remember; `if`(y<0 or y>n or t=3, 0,
      `if`(n=0, 1, b(n-1, y, `if`(t=1, 2, 0))+`if`(n>1, b(n-2,
       y, 0)+b(n-2, y+1, 1), 0)+b(n-1, y-1, `if`(t=2, 3, 0))))
    end:
a:= n-> b(n, 0$2):
seq(T(n), n=0..40); # Alois P. Heinz, Sep 16 2014

Mathematica

b[n_, y_, t_] := b[n, y, t] = If[y<0 || y>n || t == 3, 0, If[n == 0, 1, b[n-1, y, If[t == 1, 2, 0]] + If[n>1, b[n-2, y, 0] + b[n-2, y+1, 1], 0] + b[n-1, y-1, If[t == 2, 3, 0]]]]; a[n_] := b[n, 0, 0]; Table[a[n], {n, 0, 40}] (* Jean-François Alcover, May 27 2015, after Alois P. Heinz *)

Formula

G.f. G = G(z) satisfies G = 1 + z*G + z^2*G + z^3*G*(G - z).

D-finite with recurrence +(n+3)*a(n) +(-2*n-3)*a(n-1) -n*a(n-2) +(-2*n+3)*a(n-3) +3*(n-3)*a(n-4) +(-2*n+9)*a(n-5) +2*(-n+6)*a(n-6) +(n-9)*a(n-8)=0. - R. J. Mathar, Sep 29 2021