This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A280548 #6 Apr 21 2020 12:58:39 %S A280548 0,0,50,382,1764,6502,20334,56102,141398,332810,743966,1598198, %T A280548 3328362,6763114 %N A280548 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 two elements, and with new values introduced in order 0 sequentially upwards. %C A280548 Diagonal of A280554. %e A280548 Some solutions for n=4 %e A280548 ..0..1..0..1. .0..1..1..1. .0..1..0..0. .0..1..0..0. .0..0..1..0 %e A280548 ..1..1..1..0. .1..0..0..1. .0..1..0..1. .1..0..0..1. .1..1..0..1 %e A280548 ..0..1..0..1. .0..1..1..0. .1..0..1..0. .0..1..0..1. .0..0..0..0 %e A280548 ..0..0..1..0. .1..0..0..1. .0..0..1..0. .1..0..1..0. .1..1..0..1 %Y A280548 Cf. A280554. %K A280548 nonn %O A280548 1,3 %A A280548 _R. H. Hardin_, Jan 05 2017