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 A268070 #4 Jan 25 2016 21:10:11 %S A268070 2,15,159,2191,30295,421471,5797959,79367143,1079774311,14630901175, %T A268070 197520668295,2659138662775,35714778101863,478783751931415, %U A268070 6408527754114375,85670414104756855,1144076540594898727 %N A268070 Number of nX2 0..3 arrays with every repeated value in every row and column unequal to the previous repeated value, and new values introduced in row-major sequential order. %C A268070 Column 2 of A268073. %H A268070 R. H. Hardin, <a href="/A268070/b268070.txt">Table of n, a(n) for n = 1..210</a> %F A268070 Empirical: a(n) = 26*a(n-1) -109*a(n-2) -1668*a(n-3) +10384*a(n-4) +30340*a(n-5) -193268*a(n-6) -33480*a(n-7) +882432*a(n-8) -461376*a(n-9) -1073088*a(n-10) +839808*a(n-11) for n>13 %e A268070 Some solutions for n=5 %e A268070 ..0..1....0..1....0..1....0..1....0..0....0..1....0..1....0..1....0..1....0..1 %e A268070 ..0..2....0..0....2..3....1..0....1..0....1..2....0..0....1..2....1..1....2..3 %e A268070 ..2..1....1..2....2..3....2..0....1..1....0..3....2..2....1..3....2..3....2..2 %e A268070 ..2..0....0..3....1..2....2..1....0..0....0..1....3..3....3..3....2..3....0..2 %e A268070 ..1..0....1..1....0..2....0..2....2..3....1..2....1..2....0..0....3..1....3..3 %Y A268070 Cf. A268073. %K A268070 nonn %O A268070 1,1 %A A268070 _R. H. Hardin_, Jan 25 2016