

A182888


Triangle read by rows: T(n,k) is the number of weighted lattice paths in L_n having k (1,0)steps at level 0. These 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.


2



1, 0, 1, 1, 0, 1, 2, 2, 0, 1, 3, 4, 3, 0, 1, 8, 7, 6, 4, 0, 1, 17, 20, 12, 8, 5, 0, 1, 38, 44, 36, 18, 10, 6, 0, 1, 89, 104, 82, 56, 25, 12, 7, 0, 1, 206, 253, 204, 132, 80, 33, 14, 8, 0, 1, 485, 604, 513, 344, 195, 108, 42, 16, 9, 0, 1, 1152, 1466, 1262, 891, 530, 272, 140, 52, 18, 10, 0, 1
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OFFSET

0,7


COMMENTS

Sum of entries in row n is A051286(n).
T(n,0)=A182889(n).
Sum(k*T(n,k), k=0..n)=A182890(n).


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

Table of n, a(n) for n=0..77.


FORMULA

G.f.: G(t,z) =1/( ztz+sqrt((1+z+z^2)(13z+z^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 hH and Hh, have exactly two (1,0)steps at level 0.
Triangle starts:
1;
0,1;
1,0,1;
2,2,0,1;
3,4,3,0,1;
8,7,6,4,0,1.


MAPLE

G:=1/(zt*z+sqrt((1+z+z^2)*(13*z+z^2))): Gser:=simplify(series(G, z=0, 14)): for n from 0 to 11 do P[n]:=sort(coeff(Gser, z, n)) od: for n from 0 to 11 do seq(coeff(P[n], t, k), k=0..n) od; # yields sequence in triangular form


CROSSREFS

Cf. A051286, A182889, A182890.
Sequence in context: A124394 A086460 A136431 * A296068 A144064 A172236
Adjacent sequences: A182885 A182886 A182887 * A182889 A182890 A182891


KEYWORD

nonn,tabl


AUTHOR

Emeric Deutsch, Dec 11 2010


STATUS

approved



