%I #6 Apr 21 2020 12:58:16
%S 0,4,21,80,225,548,1211,2512,4989,9604,18073,33432,61035,110276,
%T 197581,351568,621945
%N Number of n X n 0..1 arrays with no element equal to more than one of its horizontal and vertical neighbors, with the exception of exactly one element, and with new values introduced in order 0 sequentially upwards.
%C Diagonal of A280440.
%e Some solutions for n=4
%e ..0..0..1..0. .0..1..0..1. .0..1..0..1. .0..0..1..1. .0..0..1..0
%e ..1..1..0..1. .1..0..1..0. .1..0..1..0. .0..1..0..0. .1..0..1..0
%e ..0..0..1..0. .0..1..0..0. .0..1..0..1. .1..0..1..1. .0..1..0..1
%e ..0..1..0..1. .1..0..1..0. .0..1..1..0. .0..1..0..0. .0..1..0..1
%Y Cf. A280440.
%K nonn
%O 1,2
%A _R. H. Hardin_, Jan 03 2017