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 A274726 #4 Jul 03 2016 20:16:01 %S A274726 122,1536,5728,66132,771300,8960464,105328812,1237030912,14505195904, %T A274726 170291855288,1998101079148,23450606174376,275190816259724, %U A274726 3229562907115528,37899889658769384,444774756528884068 %N A274726 Number of nX6 0..2 arrays with no element equal to any value at offset (-1,-2) (-2,-1) or (-1,0) and new values introduced in order 0..2. %C A274726 Column 6 of A274728. %H A274726 R. H. Hardin, <a href="/A274726/b274726.txt">Table of n, a(n) for n = 1..210</a> %F A274726 Empirical: a(n) = 3*a(n-1) +78*a(n-2) +250*a(n-3) +558*a(n-4) -937*a(n-5) -4256*a(n-6) -7991*a(n-7) -3472*a(n-8) +31381*a(n-9) -11144*a(n-10) +42683*a(n-11) -198936*a(n-12) +231086*a(n-13) -131301*a(n-14) +70502*a(n-15) -27827*a(n-16) +159651*a(n-17) -217780*a(n-18) +120250*a(n-19) -55920*a(n-20) -17125*a(n-21) +26805*a(n-22) -25487*a(n-23) +30226*a(n-24) -15183*a(n-25) +5503*a(n-26) -1930*a(n-27) +371*a(n-28) -65*a(n-29) +8*a(n-30) for n>35 %e A274726 Some solutions for n=4 %e A274726 ..0..1..2..2..2..1. .0..1..1..2..0..2. .0..1..0..2..0..2. .0..1..0..2..0..2 %e A274726 ..1..0..1..0..1..0. .2..0..2..0..2..1. .1..0..2..0..2..0. .2..0..1..0..2..0 %e A274726 ..2..1..0..1..0..1. .0..1..0..2..1..2. .0..2..0..2..0..2. .0..1..0..2..0..2 %e A274726 ..0..0..1..2..2..2. .2..0..1..0..2..1. .2..0..1..0..2..1. .2..0..1..0..2..1 %Y A274726 Cf. A274728. %K A274726 nonn %O A274726 1,1 %A A274726 _R. H. Hardin_, Jul 03 2016