A180752 Half the number of nX3 binary arrays with each element equal to at least two neighbors.

0, 1, 1, 2, 3, 7, 14, 31, 67, 148, 325, 717, 1580, 3485, 7685, 16950, 37383, 82451, 181850, 401083, 884615, 1951080, 4303241, 9491097, 20933272, 46169785, 101830665, 224594602, 495358987, 1092548639, 2409691878, 5314742743

Offset: 1

Author

R. H. Hardin Sep 20 2010

Keywords

• nonn

Comments

Column 3 of A180760

Links

• R. H. Hardin, Table of n, a(n) for n=1..99

Formula

Empirical: a(n) = 2*a(n-1) + a(n-2) - a(n-3) - a(n-5).

Empirical: G.f.: -x^2*(-1+x+x^3+x^2) / ( (x-1)*(1+x)*(x^3+2*x-1) ). a(n)-a(n-2) = A052980(n-3). - R. J. Mathar, Mar 24 2018