A220324 - OEIS

%I #8 Jul 31 2018 08:53:27

%S 2,16,92,508,2788,15316,84196,462940,2545492,13996468,76959844,

%T 423164812,2326777444,12793817140,70346976484,386803802332,

%U 2126845944052,11694491219668,64302318307108,353567167818892,1944093859291588

%N Equals two maps: number of n X 3 binary arrays indicating the locations of corresponding elements equal to exactly two of their horizontal and antidiagonal neighbors in a random 0..1 n X 3 array.

%C Column 3 of A220328.

%H R. H. Hardin, <a href="/A220324/b220324.txt">Table of n, a(n) for n = 1..210</a>

%F Empirical: a(n) = 7*a(n-1) - 9*a(n-2) + 3*a(n-3) + 6*a(n-4).

%F Empirical g.f.: 2*x*(1 + x - x^2 + x^3) / (1 - 7*x + 9*x^2 - 3*x^3 - 6*x^4). - _Colin Barker_, Jul 31 2018

%e Some solutions for n=3:

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

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

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

%Y Cf. A220328.

%K nonn

%O 1,1

%A _R. H. Hardin_, Dec 10 2012