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A243873 Number of Dyck paths of semilength n having exactly 3 (possibly overlapping) occurrences of the consecutive steps UDUUUDDDUD (with U=(1,1), D=(1,-1)). 2
1, 5, 23, 105, 472, 2118, 9446, 41847, 184256, 806740, 3514298, 15238732, 65803650, 283077978, 1213561196, 5186141801, 22098720181, 93913940321, 398127653185, 1683928072645, 7107304159469, 29938529102885, 125880340885997, 528371537192555, 2214227613719264 (list; graph; refs; listen; history; text; internal format)
OFFSET

13,2

LINKS

Alois P. Heinz, Table of n, a(n) for n = 13..400

MAPLE

b:= proc(x, y, t) option remember; `if`(y<0 or y>x, 0, `if`(x=0, 1,

     series(b(x-1, y+1, [2, 2, 4, 5, 6, 2, 4, 2, 10, 2][t])+`if`(t=10,

      z, 1)*b(x-1, y-1, [1, 3, 1, 3, 3, 7, 8, 9, 1, 3][t]), z, 4)))

    end:

a:= n-> coeff(b(2*n, 0, 1), z, 3):

seq(a(n), n=13..45);

CROSSREFS

Column k=3 of A243881.

Sequence in context: A290924 A026760 A064914 * A239406 A107839 A270530

Adjacent sequences:  A243870 A243871 A243872 * A243874 A243875 A243876

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Jun 13 2014

STATUS

approved

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Last modified July 8 03:38 EDT 2020. Contains 335504 sequences. (Running on oeis4.)