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%I #7 Apr 06 2020 00:29:17
%S 2,11,153,4917,366606,66730314,31357593706
%N Number of n X n 0,1 arrays indicating 2 X 2 subblocks of some larger (n+1) X (n+1) binary array having two adjacent 1's and two adjacent 0's, with rows and columns of the latter in lexicographically nondecreasing order.
%C Diagonal of A227333.
%e Some solutions for n=4
%e ..0..0..0..0....0..0..1..0....0..1..1..1....0..0..1..0....0..1..1..0
%e ..0..0..0..0....1..1..0..0....1..0..1..1....0..0..1..0....0..1..1..0
%e ..1..0..1..0....0..1..0..0....0..0..1..1....1..0..1..0....1..0..1..1
%e ..0..1..0..0....0..0..0..0....0..1..0..0....1..0..0..1....0..0..1..0
%Y Cf. A227333.
%K nonn
%O 1,1
%A _R. H. Hardin_ Jul 07 2013