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 A186160 #8 Jul 22 2025 10:16:50 %S A186160 0,7,702,751266,5033988714,268995986029278 %N A186160 1/4 the number of n X n 0..3 arrays with every element equal to exactly one or two of its horizontal and vertical neighbors. %C A186160 Diagonal of A186168 %e A186160 Some solutions for 4X4 with a(1,1)=0 %e A186160 ..0..2..0..2....0..0..2..0....0..2..1..1....0..0..2..2....0..2..2..1 %e A186160 ..0..2..0..2....0..0..2..0....0..2..0..0....0..2..1..2....0..0..0..1 %e A186160 ..1..2..3..3....2..3..3..3....2..1..1..0....2..2..1..0....2..3..3..1 %e A186160 ..1..1..1..1....2..3..2..2....2..2..1..0....3..3..3..0....2..3..0..0 %K A186160 nonn %O A186160 1,2 %A A186160 _R. H. Hardin_ Feb 13 2011