A180762 Half the number of nX2 binary arrays with each element equal to at least one neighbor.

1, 3, 11, 34, 111, 361, 1172, 3809, 12377, 40218, 130687, 424661, 1379916, 4483973, 14570461, 47346034, 153848731, 499924281, 1624480652, 5278674169, 17152805697, 55737242698, 181115572487, 588526611821, 1912389796556, 6214221516093

Offset: 1

Author

R. H. Hardin Sep 20 2010

Keywords

• nonn

Comments

Column 2 of A180771

Links

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

Formula

Empirical: a(n) = 3*a(n-1) + a(n-2) - 2*a(n-4).

Empirical g.f.: x*(1-x)*(1+x+2*x^2)/(1-3*x-x^2+2*x^4). - Colin Barker, Feb 22 2012