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 A206877 #8 Jul 22 2025 19:45:51 %S A206877 2,16,230,6478,472412,87541530,37121455086,35861331864570, %T A206877 81188767942820548,433324879893854403222,5417399373066905672590966, %U A206877 158241198424834434935170407538,10811858970416460513671922192330804 %N A206877 Number of n X n 0..1 arrays avoiding 0 1 0 horizontally and 1 0 1 vertically. %C A206877 Diagonal of A206883 %e A206877 Some solutions for n=4 %e A206877 ..1..0..0..1....1..0..0..0....0..1..1..1....1..0..1..1....0..0..1..1 %e A206877 ..1..1..0..0....1..1..1..1....0..0..0..0....0..0..1..1....1..1..0..1 %e A206877 ..1..0..0..0....1..0..1..1....1..0..0..0....0..1..1..1....1..0..0..0 %e A206877 ..1..0..0..1....1..0..1..1....0..1..1..1....0..0..0..1....0..0..0..0 %K A206877 nonn %O A206877 1,1 %A A206877 _R. H. Hardin_ Feb 13 2012