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 A208469 #6 Jul 22 2025 21:23:07 %S A208469 15,4140,4150760,10318694804,50996571454200,440379403449903222, %T A208469 6092197983646590702604 %N A208469 Number of 4Xn nonnegative integer arrays with new values 0 upwards introduced in row major order and no element equal to more than two of its immediate leftward or upward or right-upward antidiagonal neighbors. %C A208469 Row 4 of A208466 %e A208469 Some solutions for n=4 %e A208469 ..0..0..0..0....0..0..0..0....0..0..0..0....0..0..0..0....0..0..0..0 %e A208469 ..0..1..2..0....0..1..0..2....1..2..0..0....1..0..1..1....0..1..0..0 %e A208469 ..0..0..0..0....1..0..0..0....0..0..1..0....0..1..2..0....0..0..1..0 %e A208469 ..1..0..1..2....0..1..0..2....0..0..0..0....0..0..0..0....0..0..0..0 %K A208469 nonn %O A208469 1,1 %A A208469 _R. H. Hardin_ Feb 27 2012