A025245 a(n) = (1/2)*s(n+3), where s = A025244.

1, 2, 5, 11, 26, 65, 163, 416, 1081, 2837, 7516, 20089, 54077, 146478, 398997, 1092215, 3003014, 8289569, 22964919, 63828252, 177931665, 497367721, 1393768952, 3914793457, 11019379609, 31079140922, 87818240869, 248571086403, 704722488690

Offset

1,2

Links

Table of n, a(n) for n=1..29.

Paul Barry, On a Generalization of the Narayana Triangle, J. Int. Seq. 14 (2011) # 11.4.5.

Formula

G.f.: (1-x-x^2-4*x^3-sqrt(1-2*x-x^2-6*x^3+x^4))/(4*x^3). - Michael Somos, Jun 08 2000

Conjecture: (n+3)*a(n) +(-2*n-3)*a(n-1) -n*a(n-2) +3*(-2*n+3)*a(n-3) +(n-3)*a(n-4)=0. - R. J. Mathar, Feb 25 2015

Prog

(PARI) a(n)=polcoeff((-sqrt(1-2*x-x^2-6*x^3+x^4+x^4*O(x^n)))/4, n+3)

Crossrefs

Sequence in context: A306563 A308060 A235496 * A300125 A307576 A079223

Adjacent sequences: A025242 A025243 A025244 * A025246 A025247 A025248

Keyword

nonn

Author

Clark Kimberling

Status

approved