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 A199128 #7 Jul 22 2025 13:10:45 %S A199128 1,2,6,19,70,264,1038,4155,16896,69584,289146,1211873,5111178, %T A199128 21686612,92453594,395888507,1701506820,7337867736,31739124866, %U A199128 137656095241,598476364166,2607710997676,11385288787534,49800060551081 %N A199128 Number of nX3 0..2 arrays with values 0..2 introduced in row major order, the number of instances of each value within one of each other, and no element equal to any horizontal or vertical neighbor. %C A199128 Column 3 of A199133 %H A199128 R. H. Hardin, <a href="/A199128/b199128.txt">Table of n, a(n) for n = 1..130</a> %e A199128 Some solutions for n=5 %e A199128 ..0..1..0....0..1..2....0..1..0....0..1..2....0..1..0....0..1..2....0..1..0 %e A199128 ..1..0..2....2..0..1....1..0..2....1..0..1....1..0..2....1..2..0....2..0..2 %e A199128 ..0..2..1....0..1..2....0..2..1....0..2..0....2..1..0....2..0..1....0..1..0 %e A199128 ..2..0..2....1..2..0....2..1..2....2..1..2....1..2..1....1..2..0....1..2..1 %e A199128 ..1..2..1....2..0..1....0..2..1....0..2..1....2..0..2....0..1..2....2..1..2 %K A199128 nonn %O A199128 1,2 %A A199128 _R. H. Hardin_ Nov 03 2011