A020865 Number of forests in Moebius ladder M_n.

0, 4, 38, 328, 2686, 21224, 163982, 1249784, 9447102, 71056840, 532854638, 3988597144, 29822927134, 222836912744, 1664351910350, 12427793513528, 92784673372542, 692656225953544, 5170521713987630, 38595421782328024, 288089831076277726, 2150375933904641960

Offset

0,2

Links

Colin Barker, Table of n, a(n) for n = 0..1000

J. P. McSorley, Counting structures in the Moebius ladder, Discrete Math., 184 (1998), 137-164.

Index entries for linear recurrences with constant coefficients, signature (16,-87,200,-208,96,-16).

Formula

a(n) = (4+sqrt(12))^n+(4-sqrt(12))^n+2^n-(5/2+1/2*sqrt(17))^n-(5/2-1/2*sqrt(17))^n-1.

G.f.: 2*x*(2-13*x+34*x^2-28*x^3+8*x^4) / ( (x-1)*(2*x-1)*(4*x^2-8*x+1)*(2*x^2-5*x+1) ).

Prog

(PARI) concat(0, Vec(2*x*(8*x^4-28*x^3+34*x^2-13*x+2)/((x-1)*(2*x-1)*(2*x^2-5*x+1)*(4*x^2-8*x+1)) + O(x^30))) \\ Colin Barker, Aug 02 2015

Crossrefs

Sequence in context: A196945 A240287 A092642 * A240378 A220807 A221021

Adjacent sequences: A020862 A020863 A020864 * A020866 A020867 A020868

Keyword

nonn,easy

Author

N. J. A. Sloane

Status

approved