

A182898


Triangle read by rows: T(n,k) is the number of weighted lattice paths in L_n having k returns to the horizontal axis (both from above and below). The members of L_n are paths of weight n that start at (0,0) , end on the horizontal axis and whose steps are of the following four kinds: an (1,0)step with weight 1, an (1,0)step with weight 2, a (1,1)step with weight 2, and a (1,1)step with weight 1. The weight of a path is the sum of the weights of its steps.


1



1, 1, 2, 3, 2, 5, 6, 8, 18, 13, 46, 4, 21, 112, 20, 34, 262, 80, 55, 600, 268, 8, 89, 1356, 816, 56, 144, 3046, 2324, 280, 233, 6832, 6320, 1144, 16, 377, 15354, 16620, 4136, 144, 610, 34658, 42652, 13728, 864, 987, 78706, 107520, 42816, 4144, 32, 1597, 180000, 267564, 127392, 17264, 352
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OFFSET

0,3


COMMENTS

Sum of entries in row n is A051286(n).
T(n,0)=A000045(n+1) (the Fibonacci numbers).


REFERENCES

M. Bona and A. Knopfmacher, On the probability that certain compositions have the same number of parts, Ann. Comb., 14 (2010), 291306.
E. Munarini, N. Zagaglia Salvi, On the rank polynomial of the lattice of order ideals of fences and crowns, Discrete Mathematics 259 (2002), 163177.


LINKS



FORMULA

G.f.: G(t,z) =1/[1zz^22tz^3*c], where c satisfies c = 1+zc+z^2*c+z^3*c^2.
The trivariate g.f. H=H(t,s,z), where t (s) marks (1,1)returns ((1,1)returns) to the horizontal axis, and z marks weight is given by H=1+zH+z^2*H+(t+s)z^3*cH, where c satisfies c = 1+zc+z^2*c+z^3*c^2.


EXAMPLE

T(3,1)=2. Indeed, denoting by h (H) the (1,0)step of weight 1 (2), and u=(1,1), d=(1,1), the five paths of weight 3 are ud, du, hH, Hh, and hhh; two of them, namely ud and du, have 1 return to the horizontal axis.
Triangle starts:
1;
1;
2;
3,2;
5,6;
8,18;
13,46,4;
21,112,20;


MAPLE

eq := c = 1+z*c+z^2*c+z^3*c^2: c := RootOf(eq, c): G := 1/(1zz^22*t*z^3*c): Gser := simplify(series(G, z = 0, 20)): for n from 0 to 16 do P[n] := sort(coeff(Gser, z, n)) end do: for n from 0 to 16 do seq(coeff(P[n], t, k), k = 0 .. floor((1/3)*n)) end do; # yields sequence in triangular form


CROSSREFS



KEYWORD

nonn,tabf


AUTHOR



STATUS

approved



