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

1,2

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]

Crossrefs

Sequence in context: A052471 A037496 A355364 * A134326 A295546 A361435

Adjacent sequences: A180759 A180760 A180761 * A180763 A180764 A180765

Keyword

nonn

Author

R. H. Hardin Sep 20 2010

Status

approved