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 A280956 #4 Jan 11 2017 15:13:44 %S A280956 4,42,241,1554,9899,63085,402077,2562733,16334111,104108376,663554669, %T A280956 4229292041,26956196587,171810442122,1095066516245,6979614612419, %U A280956 44485900541127,283539343806484,1807191908208865,11518481171610485 %N A280956 Number of nX3 0..2 arrays with no element equal to more than one of its horizontal, vertical and antidiagonal neighbors and with new values introduced in order 0 sequentially upwards. %C A280956 Column 3 of A280961. %H A280956 R. H. Hardin, <a href="/A280956/b280956.txt">Table of n, a(n) for n = 1..210</a> %F A280956 Empirical: a(n) = 5*a(n-1) +8*a(n-2) +5*a(n-3) +4*a(n-4) -35*a(n-5) +2*a(n-6) +71*a(n-7) -11*a(n-8) -38*a(n-9) +6*a(n-10) -8*a(n-11) -8*a(n-12) for n>16 %e A280956 Some solutions for n=4 %e A280956 ..0..1..0. .0..0..1. .0..1..2. .0..1..2. .0..1..0. .0..0..1. .0..1..1 %e A280956 ..1..2..2. .2..2..0. .1..2..0. .2..0..0. .0..2..0. .2..1..2. .0..2..0 %e A280956 ..0..1..0. .0..1..2. .0..1..2. .2..1..2. .2..1..2. .2..0..1. .1..0..1 %e A280956 ..1..0..1. .1..0..2. .2..1..0. .0..0..1. .1..0..0. .0..2..2. .2..2..0 %Y A280956 Cf. A280961. %K A280956 nonn %O A280956 1,1 %A A280956 _R. H. Hardin_, Jan 11 2017