A020880 Number of strong elementary edge-subgraphs in Moebius ladder M_n.

6, 21, 26, 81, 129, 349, 650, 1614, 3281, 7772, 16565, 38265, 83635, 190656, 422266, 955967, 2131986, 4809229, 10764221, 24235939, 54347662, 122246248, 274396853, 616899656, 1385407029

Offset

2,1

Links

Table of n, a(n) for n=2..26.

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

Formula

Conjectures from Colin Barker, Dec 20 2019: (Start)

G.f.: x^2*(6 + 9*x - 46*x^2 - 22*x^3 + 74*x^4 + 16*x^5 - 38*x^6 - 3*x^7 + 6*x^8) / ((1 - x)*(1 + x)*(1 + x - x^2)*(1 - x - x^2)*(1 - 2*x - x^2 + x^3)).

a(n) = 2*a(n-1) + 5*a(n-2) - 9*a(n-3) - 8*a(n-4) + 12*a(n-5) + 5*a(n-6) - 6*a(n-7) - a(n-8) + a(n-9) for n>10.

(End)

Crossrefs

Sequence in context: A369969 A229498 A164698 * A046467 A132184 A143322

Adjacent sequences: A020877 A020878 A020879 * A020881 A020882 A020883

Keyword

nonn,more

Author

N. J. A. Sloane

Extensions

a(6)-a(26) from Sean A. Irvine, May 01 2019

Status

approved