A109979 Triangle read by rows: T(n,k) (0<=k<=n) is the number of Delannoy paths of length n, having k (1,1)-steps on 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)).

1, 2, 1, 8, 4, 1, 36, 20, 6, 1, 172, 104, 36, 8, 1, 852, 552, 212, 56, 10, 1, 4324, 2968, 1236, 368, 80, 12, 1, 22332, 16104, 7164, 2336, 580, 108, 14, 1, 116876, 87976, 41372, 14512, 3980, 856, 140, 16, 1, 618084, 483192, 238356, 88848, 26372, 6312, 1204, 176

Offset: 0

Author

Emeric Deutsch, Jul 06 2005

Keywords

• nonn
• tabl

Comments

Row sums are the central Delannoy numbers (A001850).

First column yields A109980.

sum(k*T(n,k),k=0..n) = A001109(n).

Examples

			T(2,1)=4 because we have DNE, DEN, NED and END.
Triangle begins:
1;
2,1;
8,4,1;
36,20,6,1;
		

Links

• Robert A. Sulanke, Objects Counted by the Central Delannoy Numbers, Journal of Integer Sequences, Volume 6, 2003, Article 03.1.5.

Crossrefs

Cf. A001850, A109980, A001109.

Programs

Maple

G:=(t*z-z+sqrt(1-6*z+z^2))/(1-6*z+2*t*z^2-t^2*z^2): Gser:=simplify(series(G,z=0,13)): P[0]:=1: for n from 1 to 10 do P[n]:=coeff(Gser,z^n) od: for n from 0 to 10 do seq(coeff(t*P[n],t^k),k=1..n+1) od; # yields sequence in triangular form

Formula

G.f.: [tz-z+sqrt(1-6z+z^2)]/(1-6z+2tz^2-t^2*z^2).