login
Triangle read by rows: T(n,k) (0<=k<=n) is the number of Schroeder paths of length 2n, having k (1,0)-steps on the lines y=0 and y=1 (a Schroeder path of length 2n is a path from (0,0) to (2n,0), consisting of steps U=(1,1), D=(1,-1) and H=(2,0) and never going below the x-axis).
1

%I #5 Mar 30 2012 17:36:06

%S 1,1,1,2,3,1,6,9,6,1,22,32,25,10,1,90,128,105,55,15,1,394,552,462,271,

%T 105,21,1,1806,2504,2118,1317,602,182,28,1,8558,11776,10026,6456,3235,

%U 1204,294,36,1,41586,56896,48658,32068,17019,7149,2226,450,45,1,206098

%N Triangle read by rows: T(n,k) (0<=k<=n) is the number of Schroeder paths of length 2n, having k (1,0)-steps on the lines y=0 and y=1 (a Schroeder path of length 2n is a path from (0,0) to (2n,0), consisting of steps U=(1,1), D=(1,-1) and H=(2,0) and never going below the x-axis).

%C Row sums are the large Schroeder numbers (A006318). First column yields the large Schroeder numbers (A006318). sum(k*T(n,k),k=0..n)=A110190(n).

%F G.f.=(1-tz-zR)/[(1-tz)^2-z-z(1-tz)R], where R=.1+zR+zR^2=[1-z-sqrt(1-6z+z^2)]/(2z) is the g.f. of the large Schroeder numbers (A006318).

%e T(3,2)=6 because we have HHUD, HUHD, HUDH, UDHH, UHDH and UHHD.

%e Triangle starts:

%e 1;

%e 1,1;

%e 2,3,1;

%e 6,9,6,1;

%e 22,32,25,10,1;

%p R:=(1-z-sqrt(1-6*z+z^2))/2/z: G:=(1-t*z-z*R)/((1-t*z)^2-z-z*(1-t*z)*R): 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

%Y Cf. A006318, A110190.

%K nonn,tabl

%O 0,4

%A _Emeric Deutsch_, Jul 15 2005