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%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