Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #5 Dec 18 2015 18:18:54
%S 1,1,145,57721,41855199,569620472894,7361174970568815,
%T 1484662166072017164173,589336120060277543986621142
%N Number of n X n 0..2n-2 arrays with upper left zero and lower right 2n-2 and each element differing from its horizontal and vertical neighbors by one or two.
%C Diagonal of A265447.
%e Some solutions for n=4
%e ..0..2..4..2....0..2..1..2....0..2..0..1....0..2..3..4....0..2..4..5
%e ..2..0..2..4....2..1..3..4....2..3..1..2....1..3..1..3....2..3..5..6
%e ..1..2..4..5....3..2..4..5....0..1..2..4....3..1..2..4....4..5..6..4
%e ..3..4..5..6....5..4..5..6....1..3..4..6....1..2..4..6....2..3..4..6
%Y Cf. A265447.
%K nonn
%O 1,3
%A _R. H. Hardin_, Dec 09 2015