

A138158


Triangle read by rows: T(n,k) is the number of ordered trees with n edges and path length k; 0 <= k <= n(n+1)/2.


7



1, 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 2, 1, 1, 0, 0, 0, 0, 1, 3, 3, 3, 2, 1, 1, 0, 0, 0, 0, 0, 1, 4, 6, 7, 7, 5, 5, 3, 2, 1, 1, 0, 0, 0, 0, 0, 0, 1, 5, 10, 14, 17, 16, 16, 14, 11, 9, 7, 5, 3, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 1, 6, 15, 25, 35, 40, 43, 44, 40, 37, 32, 28, 22, 18, 13, 11, 7, 5, 3, 2, 1, 1
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OFFSET

0,12


COMMENTS

T(n,k) is the number of Dyck paths of semilength n for which the sum of the heights of the vertices that terminate an upstep (i.e. peaks and doublerises) is k. Example: T(4,7)=3 because we have UUDUDUDD, UDUUUDDD and UUUDDDUD.
See related triangle A227543.
Row n contains 1+n(n+1)/2 terms.
The maximum in each row of the triangle is A274291.  Torsten Muetze, Nov 28 2018


LINKS

Seiichi Manyama, Rows n = 0..38, flattened
Ron M. Adin, Yuval Roichman, On maximal chains in the noncrossing partition lattice, arXiv:1201.4669 [math.CO], 2012.
Luca Ferrari, Unimodality and Dyck paths, arXiv:1207.7295 [math.CO], 2012.
FindStat  Combinatorial Statistic Finder, The bounce statistic of a Dyck path, The dinv statistic of a Dyck path, The area of a Dyck path.


FORMULA

G.f. G(t,z) satisfies G(t,z) = 1+t*z*G(t,z)*G(t,t*z).
Row generating polynomials P[n]=P[n](t) are given by P[0]=1, P[n] = t * Sum( P[j]*P[nj1]*t^(n1j), j=0..n1 ) (n>=1).
Row sums are the Catalan numbers (A000108).
Sum of entries in column n = A005169(n).
Sum_{k=0..n(n+1)/2} k*T(n,k) = A000346(n1).
T(n,k) = A047998(k,n).
G.f.: 1/(1  x*y/(1  x*y^2/(1  x*y^3/(1  x*y^4/(1  x*y^5)/(1  ... ))))), a continued fraction.  Ilya Gutkovskiy, Apr 21 2017


EXAMPLE

T(2,2)=1 because /\ is the only ordered tree with 2 edges and path length 2.
Triangle starts
1,
0, 1,
0, 0, 1, 1,
0, 0, 0, 1, 2, 1, 1,
0, 0, 0, 0, 1, 3, 3, 3, 2, 1, 1,
0, 0, 0, 0, 0, 1, 4, 6, 7, 7, 5, 5, 3, 2, 1, 1,
0, 0, 0, 0, 0, 0, 1, 5, 10, 14, 17, 16, 16, 14, 11, 9, 7, 5, 3, 2, 1, 1,
0, 0, 0, 0, 0, 0, 0, 1, 6, 15, 25, 35, 40, 43, 44, 40, 37, 32, 28, 22, 18, 13, 11, 7, 5, 3, 2, 1, 1,
... [Joerg Arndt, Feb 21 2014]


MAPLE

P[0]:=1: for n to 7 do P[n]:=sort(expand(t*(sum(P[j]*P[nj1]*t^(nj1), j= 0.. n1)))) end do: for n from 0 to 7 do seq(coeff(P[n], t, j), j=0..(1/2)*n*(n+1)) end do; # yields sequence in triangular form


MATHEMATICA

nmax = 7;
P[0] = 1; P[n_] := P[n] = t*Sum[P[j]*P[nj1]*t^(nj1), {j, 0, n1}];
row[n_] := row[n] = CoefficientList[P[n] + O[t]^(n(n+1)/2 + 1), t];
T[n_, k_] := row[n][[k+1]];
Table[T[n, k], {n, 0, nmax}, {k, 0, n(n+1)/2}] // Flatten (* JeanFrançois Alcover, Jul 11 2018, from Maple *)


CROSSREFS

Cf. A227543, A000108, A005169, A000346, A047998, A274291.
Sequence in context: A321923 A064663 A025923 * A057276 A259829 A035185
Adjacent sequences: A138155 A138156 A138157 * A138159 A138160 A138161


KEYWORD

nonn,tabf


AUTHOR

Emeric Deutsch, Mar 21 2008


STATUS

approved



