A025567 a(n) = T(n,n+1), where T is the array defined in A025564.

1, 4, 13, 40, 120, 356, 1050, 3088, 9069, 26620, 78133, 229384, 673699, 1979628, 5820195, 17121312, 50394579, 148413996, 437324919, 1289330520, 3803175474, 11223840012, 33139076292, 97889042384, 289276841475, 855205791076, 2529279459099

Offset

1,2

Links

Michael De Vlieger, Table of n, a(n) for n = 1..1000

Jean-Luc Baril, Richard Genestier, Sergey Kirgizov, Pattern distributions in Dyck paths with a first return decomposition constrained by height, arXiv:1911.03119 [math.CO], 2019.

Luca Ferrari and Emanuele Munarini, Enumeration of edges in some lattices of paths, arXiv preprint arXiv:1203.6792 [math.CO], 2012 and J. Int. Seq. 17 (2014) #14.1.5

Formula

G.f.: (x^2-1-sqrt(1+x)*(x^2+2*x-1)/sqrt(1-3*x))/(2*x^3). - Mark van Hoeij, May 01 2013

Conjecture: (n+3)*a(n) +4*(-n-2)*a(n-1) +2*a(n-2) +8*(n-1)*a(n-3) +3*(n-3)*a(n-4)=0. - R. J. Mathar, Apr 03 2015

Conjecture: (n-1)*(n-2)*(n+3)*a(n) -2*n*(n-2)*(n+2)*a(n-1) -3*n*(n-1)^2*a(n-2)=0. - R. J. Mathar, Apr 03 2015

a(n) ~ 2 * 3^(n + 1/2) / sqrt(Pi*n). - Vaclav Kotesovec, May 02 2024

Mathematica

T[_, 0] = 1; T[1, 1] = 2; T[n_, k_] /; 0 <= k <= 2n := T[n, k] = T[n-1, k-2] + T[n-1, k-1] + T[n-1, k]; T[_, _] = 0;
a[n_] := T[n+1, n+3];
Array[a, 27] (* Jean-François Alcover, Oct 30 2018 *)

Prog

(PARI)  x='x+O('x^66); Vec((x^2-1-sqrt(1+x)*(x^2+2*x-1)/sqrt(1-3*x))/(2*x^3)) \\ Joerg Arndt, May 01 2013

Crossrefs

Pairwise sums of A014531.

Sequence in context: A027130 A027121 A238846 * A003462 A076040 A261547

Adjacent sequences: A025564 A025565 A025566 * A025568 A025569 A025570

Keyword

nonn

Author

Clark Kimberling

Status

approved