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 A280852 #6 Apr 21 2020 12:59:54 %S A280852 1,9,46,124,282,712,1738,4124,9562,21752,48730,107992,237082,516376, %T A280852 1117210 %N A280852 Number of n X n 0..2 arrays with no element equal to more than one of its king-move neighbors and with new values introduced in order 0 sequentially upwards. %C A280852 Diagonal of A280859. %e A280852 Some solutions for n=4 %e A280852 ..0..1..1..2. .0..1..2..2. .0..1..1..0. .0..1..1..2. .0..1..2..0 %e A280852 ..0..2..0..0. .0..1..0..1. .0..2..0..2. .0..2..0..0. .2..1..2..1 %e A280852 ..1..2..1..2. .2..2..0..2. .1..2..1..2. .1..2..1..1. .2..0..0..1 %e A280852 ..1..0..0..2. .0..1..1..2. .1..0..0..1. .1..0..0..2. .1..1..2..2 %Y A280852 Cf. A280859. %K A280852 nonn %O A280852 1,2 %A A280852 _R. H. Hardin_, Jan 09 2017