

A110098


Triangle read by rows: T(n,k) (0<=k<=n) is the number of Delannoy paths of length n, having k return steps to the line y=x from the line y=x+1 (i.e. E steps from the line y=x+1 to the line y=x; a Delannoy path of length n is a path from (0,0) to (n,n), consisting of steps E=(1,0), N=(0,1) and D=(1,1)).


2



1, 2, 1, 6, 6, 1, 22, 30, 10, 1, 90, 146, 70, 14, 1, 394, 714, 430, 126, 18, 1, 1806, 3534, 2490, 938, 198, 22, 1, 8558, 17718, 14002, 6314, 1734, 286, 26, 1, 41586, 89898, 77550, 40054, 13338, 2882, 390, 30, 1, 206098, 461010, 426150, 244790, 94554
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OFFSET

0,2


COMMENTS

The row sums are the central Delannoy numbers (A001850).
Column 0 yields the large Schroeder numbers (A006318).
Column 1 yields A006320.
Column k has g.f. z^k*R^(2*k+1), where R = 1+z*R+z*R^2 is the g.f. of the large Schroeder numbers (A006318).


REFERENCES

R. A. Sulanke, Objects counted by the central Delannoy numbers, J. of Integer Sequences, 6, 2003, Article 03.1.5.


LINKS

Table of n, a(n) for n=0..49.


FORMULA

T(n, k) = ((2*k+1)/(nk))*sum(binomial(nk, j)*binomial(n+k+j, nk1), j=0..nk) for k < n; T(n, n) = 1; T(n, k) = 0 for k > n. G.f. = R/(1t*z*R^2), where R = 1+z*R+z*R^2 is the g.f. of the large Schroeder numbers (A006318).
sum(k*T(n, k), k=0..n) = A110099(n).
T(n, k) = A033877(nk+1, n+k+1).  Johannes W. Meijer, Sep 05 2013


EXAMPLE

T(2, 1) = 6 because we have DN(E), N(E)D, N(E)EN, ND(E), NNE(E) and ENN(E) (the return E steps are shown between parentheses).
Triangle begins:
1;
2,1;
6,6,1;
22,30,10,1;
90,146,70,14,1;


MAPLE

T := proc(n, k) if k=n then 1 else ((2*k+1)/(nk))*sum(binomial(nk, j)*binomial(n+k+j, nk1), j=0..nk) fi end: for n from 0 to 10 do seq(T(n, k), k=0..n) od; # yields sequence in triangular form


CROSSREFS

Cf. A001850, A006318, A006320, A110099, A110107, A033877.
Sequence in context: A104684 A060538 A110183 * A130561 A157400 A091599
Adjacent sequences: A110095 A110096 A110097 * A110099 A110100 A110101


KEYWORD

nonn,tabl


AUTHOR

Emeric Deutsch, Jul 11 2005


STATUS

approved



