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 A206980 #8 Jul 22 2025 19:53:06 %S A206980 2,16,58,556,7500,119224,2926752,111202694,5582239354,398193149976, %T A206980 43178426815216,6623459579619334,1414003622686654366, %U A206980 443957184641073369216 %N A206980 Number of n X n 0..1 arrays avoiding the patterns 0 1 0 or 1 0 1 in any row, column, diagonal or antidiagonal. %C A206980 Diagonal of A206987 %e A206980 Some solutions for n=4 %e A206980 ..1..0..0..0....0..1..1..1....1..0..0..1....1..1..0..0....1..1..0..0 %e A206980 ..0..0..0..0....1..1..1..0....0..0..0..1....0..0..0..0....1..0..0..0 %e A206980 ..0..0..0..1....1..1..1..0....0..0..0..1....0..0..0..0....0..0..0..0 %e A206980 ..1..1..1..1....0..1..1..0....1..0..0..1....1..0..0..0....0..0..0..1 %K A206980 nonn %O A206980 1,1 %A A206980 _R. H. Hardin_ Feb 14 2012