A020867 Number of forests with no isolated vertices in Moebius ladder M_n.

19, 132, 851, 5298, 32068, 190711, 1120947, 6537903, 37935984, 219360837, 1265462984, 7288685420, 41935203469, 241094585397, 1385405494499, 7958227879396, 45703889854759, 262433722095008, 1506738689157576, 8650141792937245, 49657618346464719

Offset

2,1

Links

Colin Barker, Table of n, a(n) for n = 2..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 (11,-33,4,78,-39,-61,33,19,-10,-2,1).

Formula

G.f.: see G in the Maple program. - Emeric Deutsch, Dec 21 2004

Maple

G:=-(3*x^10-5*x^9-30*x^8+47*x^7+107*x^6-162*x^5-137*x^4+217*x^3+26*x^2-77*x+19)*x^2/(-1+6*x-x^2-3*x^3+x^4)/(1-4*x+x^3)/(-1+x+x^2)/(x^2-1): Gser:=series(G, x=0, 25): seq(coeff(Gser, x^n), n=2..23); # Emeric Deutsch, Dec 21 2004

Prog

(PARI) Vec(-x^2*(3*x^10 -5*x^9 -30*x^8 +47*x^7 +107*x^6 -162*x^5 -137*x^4 +217*x^3 +26*x^2 -77*x +19) / ((x -1)*(x +1)*(x^2 +x -1)*(x^3 -4*x +1)*(x^4 -3*x^3 -x^2 +6*x -1)) + O(x^30)) \\ Colin Barker, Aug 01 2015

Crossrefs

Sequence in context: A338300 A177459 A142649 * A022679 A108673 A041692

Adjacent sequences: A020864 A020865 A020866 * A020868 A020869 A020870

Keyword

nonn,easy

Author

N. J. A. Sloane

Extensions

More terms from Emeric Deutsch, Dec 21 2004

Status

approved