0,6

Row n has 1+floor((n+1)^2/4) terms, the first n of which are equal to 0. Row sums yield the Catalan numbers (A000108). T(n,n)=2^(n-1)=A011782(n)=A000079(n-1) for n>=1. Sum(k*T(n,k),k>=0)=4^(n-1)=A000302(n-1).

Also number of parallelogram polyominoes of semiperimeter n+1 and having area equal to k. Example: T(3,4)=1 because the square with side 2 is the only parallelogram polyomino with semiperimeter 4 and area 4. - Emeric Deutsch (deutsch(AT)duke.poly.edu), Apr 07 2007

M. P. Delest and J. M. Fedou, Counting polyominoes using attribute grammars, Lecture Notes in Computer Science, vol. 461, pp. 46-60, Springer, Berlin, 1990.

M. P. Delest and J. M. Fedou, Attribute grammars are useful for combinatorics, Theor. Comp. Sci., 98, 1992, 65-76.

M. P. Delest and J. M. Fedou, Enumeration of skew Ferrers diagrams, Discrete Math., 112, 1993, 65-79.

G.f.=G(t,z)=H(t,1,z), where H(t,x,z)=1+z[H(t,tx,z)-1+tx]H(t,x,z) (H(t,x,z) is the trivariate g.f. for Dyck paths according to sum of the height of the peaks, number of peaks and semilength, marked by t,x and z, respectively).

T(4,5)=4 because we have UDUUDUDD, UUDUDDUD, UUDUUDDD and UUUDDUDD.

Triangle starts:

1;

0,1;

0,0,2;

0,0,0,4,1;

0,0,0,0,8,4,2;

0,0,0,0,0,16,12,9,4,1;

H:=1/(1-z*h[1]+z-z*t*x): for n from 1 to 11 do h[n]:=1/(1-z*h[n+1]+z-z*t^(n+1)*x) od: h[12]:=0: x:=1: G:=simplify(H): Gser:=simplify(series(G, z=0, 11)): for n from 0 to 9 do P[n]:=sort(coeff(Gser, z, n)) od: for n from 0 to 9 do seq(coeff(P[n], t, j), j=0..floor((n+1)^2/4)) od; # yields sequence in triangular form

Cf. A000108, A011782, A000079, A000302.

Sequence in context: A114855 A100951 A011991 this_sequence A110173 A131427 A153198

Adjacent sequences: A129180 A129181 A129182 this_sequence A129184 A129185 A129186

nonn,tabf

Emeric Deutsch (deutsch(AT)duke.poly.edu), Apr 07 2007