

A334787


a(n) is the total number of down steps before the first up step in all 4_3Dyck paths of length 5*n. A 4_3Dyck path is a lattice path with steps (1, 4), (1, 1) that starts and ends at y = 0 and stays above the line y = 3.


4



0, 6, 34, 251, 2105, 19040, 181076, 1784728, 18067803, 186754590, 1962728460, 20910164730, 225308533359, 2451112021568, 26885549373440, 297008527319440, 3301615350645935, 36903975448964670, 414518195957729886, 4676429192392769805, 52965796433899543810
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OFFSET

0,2


LINKS

Table of n, a(n) for n=0..20.
A. Asinowski, B. Hackl, and S. Selkirk, Down step statistics in generalized Dyck paths, arXiv:2007.15562 [math.CO], 2020.


FORMULA

a(0) = 0 and a(n) = 4*binomial(5*n, n)/(n+1)  binomial(5*n+3, n)/(n+1) for n > 0.


EXAMPLE

For n = 1, there are the 4_3Dyck paths UDDDD, DUDDD, DDUDD, DDDUD. Before the first up step there are a(1) = 0 + 1 + 2 + 3 = 6 down steps in total.


MATHEMATICA

a[0] = 0; a[n_] := 4 * Binomial[5*n, n]/(n+1)  Binomial[5*n+3, n]/(n+1); Array[a, 21, 0]


CROSSREFS

Cf. A001764, A002293, A002294, A334785, A334786.
Sequence in context: A230331 A267242 A197436 * A302148 A218685 A108432
Adjacent sequences: A334784 A334785 A334786 * A334788 A334789 A334790


KEYWORD

nonn,easy


AUTHOR

Sarah Selkirk, May 11 2020


STATUS

approved



