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 A208387 #7 Jul 22 2025 21:19:03 %S A208387 5,117,3042,79092,2056392,53466192,1390120992,36143145792, %T A208387 939721790592,24432766555392,635251930440192,16516550191444992, %U A208387 429430304977569792,11165187929416814592,290294886164837179392,7547667040285766664192 %N A208387 Number of nX3 0..2 arrays with new values 0..2 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 A208387 Column 3 of A208392 %H A208387 R. H. Hardin, <a href="/A208387/b208387.txt">Table of n, a(n) for n = 1..210</a> %F A208387 Empirical: a(n) = 26*a(n-1) for n>2 %e A208387 Some solutions for n=4 %e A208387 ..0..0..1....0..0..1....0..1..0....0..0..0....0..0..0....0..0..0....0..0..0 %e A208387 ..2..0..2....2..0..2....0..1..1....0..1..2....0..1..2....1..2..1....0..1..1 %e A208387 ..2..2..0....0..2..2....1..0..2....0..0..0....2..2..1....0..2..2....1..2..0 %e A208387 ..0..2..1....2..0..2....1..2..2....1..2..0....2..1..1....0..0..2....1..2..1 %K A208387 nonn %O A208387 1,1 %A A208387 _R. H. Hardin_ Feb 25 2012