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%I #3 Mar 31 2012 12:35:35
%S 3,28,94,154,233,300,370,428,491,552,614,676,738,800,862,924,986,1048,
%T 1110,1172,1234,1296,1358,1420,1482,1544,1606,1668,1730,1792,1854,
%U 1916,1978,2040,2102,2164,2226
%N Number of slanted 3Xn (i=1..3)X(j=i..n+i-1) 1..4 arrays with all 1s connected, all 2s connected, all 3s connected, all 4s connected, 1 in the upper left corner, 2 in the upper right corner, 3 in the lower left corner, 4 in the lower right corner, and with no element having more than 2 neighbors with the same value
%F Empirical: a(n)=2*a(n-1)-a(n-2) for n>=13
%e Some solutions for n=4
%e ...1.1.3.2.......1.2.2.2.......1.2.2.2.......1.3.2.2.......1.1.3.2....
%e .....1.3.2.2.......3.3.4.4.......2.4.4.4.......3.3.4.4.......1.3.2.3..
%e .......3.3.2.4.......3.3.4.4.......3.3.4.4.......3.3.4.4.......3.3.3.4
%e ------
%e ...1.1.3.2.......1.1.1.2.......1.1.2.2.......1.1.2.2.......1.1.1.2....
%e .....1.3.2.2.......3.3.2.4.......1.1.2.4.......1.3.2.2.......3.3.4.4..
%e .......3.3.3.4.......3.2.4.4.......3.3.4.4.......3.3.4.4.......3.3.4.4
%e ------
%e ...1.2.2.2.......1.1.2.2.......1.1.1.2.......1.1.2.2.......1.1.3.2....
%e .....3.3.2.4.......1.2.2.3.......2.2.2.4.......1.3.2.2.......1.3.4.4..
%e .......3.2.4.4.......3.3.3.4.......3.3.4.4.......3.3.3.4.......3.3.4.4
%K nonn
%O 2,1
%A _R. H. Hardin_ Sep 17 2009
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