A183324 - OEIS

%I #8 Sep 27 2013 08:22:46

%S 1,3,6,10,19,37,69,129,244,460,865,1629,3069,5779,10882,20494,38595,

%T 72681,136873,257761,485416,914136,1721505,3241945,6105241,11497411,

%U 21651966,40775058,76787731,144606925,272324269,512842017,965785884

%N Number of nX3 binary arrays with each 1 adjacent to exactly two other 1s

%C Column 3 of A183328

%H R. H. Hardin, <a href="/A183324/b183324.txt">Table of n, a(n) for n = 1..200</a>

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

%F Empirical: G.f. -x*(-1-x+x^3-x^2) / ( 1-2*x+x^2-2*x^3+x^4 ), see A033305 - _R. J. Mathar_, Sep 27 2013

%e All solutions for 4X3

%e ..0..0..0....0..0..0....1..1..1....0..0..0....0..0..0....0..0..0....1..1..0

%e ..0..0..0....0..0..0....1..0..1....1..1..1....0..1..1....1..1..0....1..1..0

%e ..1..1..0....0..0..0....1..0..1....1..0..1....0..1..1....1..1..0....0..0..0

%e ..1..1..0....0..0..0....1..1..1....1..1..1....0..0..0....0..0..0....0..0..0

%e ...

%e ..0..0..0....0..1..1....1..1..1

%e ..0..0..0....0..1..1....1..0..1

%e ..0..1..1....0..0..0....1..1..1

%e ..0..1..1....0..0..0....0..0..0

%K nonn

%O 1,2

%A _R. H. Hardin_ Jan 03 2011