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 A203968 #8 Jul 22 2025 17:41:25 %S A203968 1,7,258,34799,22100882,64449537503,847220834970347, %T A203968 50681890300309193984,13775254400039658772386790, %U A203968 17006093281906665293267116254138 %N A203968 Number of n X n 0..2 arrays with every 1 immediately preceded by 0 to the left or above, and every 2 immediately preceded by 0 1 to the left or above. %C A203968 Diagonal of A203975 %e A203968 Some solutions for n=4 %e A203968 ..0..0..0..0....0..0..1..0....0..0..0..0....0..0..1..0....0..0..1..2 %e A203968 ..1..1..0..1....1..1..0..0....0..1..1..1....1..1..0..0....0..0..0..0 %e A203968 ..0..0..0..1....0..0..1..2....1..2..0..0....0..1..0..0....0..1..0..1 %e A203968 ..1..0..1..0....0..0..0..0....2..0..1..2....0..1..2..1....0..0..0..1 %K A203968 nonn %O A203968 1,2 %A A203968 _R. H. Hardin_ Jan 08 2012