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 A208468 #6 Jul 22 2025 21:23:00 %S A208468 5,203,20746,4132120,1358524513,671329819215,468215145028629, %T A208468 440379520700561467,539586833002472556426,838156377510207185078132, %U A208468 1614568986664304552415637091,3787532565162728522045725351515 %N A208468 Number of 3Xn 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 A208468 Row 3 of A208466 %e A208468 Some solutions for n=4 %e A208468 ..0..0..0..0....0..1..2..0....0..0..0..0....0..0..0..0....0..1..0..1 %e A208468 ..0..1..0..0....0..1..0..0....0..1..1..0....0..1..2..0....0..0..0..0 %e A208468 ..1..0..1..0....0..0..1..0....0..1..0..2....1..0..0..0....1..1..1..0 %K A208468 nonn %O A208468 1,1 %A A208468 _R. H. Hardin_ Feb 27 2012