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 A280675 #4 Jan 07 2017 08:09:37 %S A280675 5,82,858,10205,119440,1401470,16438612,192831783,2261964301, %T A280675 26533504354,311245493388,3650998431229,42827250423319, %U A280675 502375841919309,5893011645334528,69126704336253119,810875921978239834 %N A280675 Number of 3Xn 0..2 arrays with no element equal to more than one of its horizontal and antidiagonal neighbors and with new values introduced in order 0 sequentially upwards. %C A280675 Row 3 of A280673. %H A280675 R. H. Hardin, <a href="/A280675/b280675.txt">Table of n, a(n) for n = 1..210</a> %F A280675 Empirical: a(n) = 11*a(n-1) +23*a(n-2) -160*a(n-3) -172*a(n-4) +690*a(n-5) +601*a(n-6) -513*a(n-7) -1314*a(n-8) -1903*a(n-9) +1720*a(n-10) +2445*a(n-11) -549*a(n-12) -998*a(n-13) +40*a(n-14) +136*a(n-15) +96*a(n-16) -32*a(n-17) -64*a(n-18) for n>20 %e A280675 Some solutions for n=4 %e A280675 ..0..1..1..0. .0..1..0..2. .0..1..1..0. .0..1..0..2. .0..0..1..0 %e A280675 ..0..2..0..2. .2..2..1..0. .2..0..1..2. .1..2..0..2. .1..2..1..2 %e A280675 ..0..1..0..1. .1..0..2..2. .0..2..0..2. .0..1..1..2. .2..0..0..1 %Y A280675 Cf. A280673. %K A280675 nonn %O A280675 1,1 %A A280675 _R. H. Hardin_, Jan 07 2017