%I #4 Mar 27 2018 14:32:54

%S 4,32,139,678,3182,15199,72514,346244,1653214,7893443,37688062,

%T 179946317,859175558,4102237937,19586633161,93518758201,446516665710,

%U 2131948036306,10179244758257,48602040050313,232056341426270,1107981178164225

%N Number of 3Xn 0..1 arrays with every element equal to 0, 1 or 2 horizontally or antidiagonally adjacent elements, with upper left element zero.

%C Row 3 of A301841.

%H R. H. Hardin, <a href="/A301843/b301843.txt">Table of n, a(n) for n = 1..210</a>

%F Empirical: a(n) = 4*a(n-1) +3*a(n-2) +3*a(n-3) +2*a(n-4) -2*a(n-5) +2*a(n-6) -7*a(n-7) -3*a(n-8) +5*a(n-9) -4*a(n-10) -3*a(n-11) +a(n-12) for n>14

%e Some solutions for n=5

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

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

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

%Y Cf. A301841.

%K nonn

%O 1,1

%A _R. H. Hardin_, Mar 27 2018