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 A274731 #4 Jul 03 2016 20:20:38 %S A274731 16,432,4132,52912,687248,8960464,116633012,1520042284,19800817976, %T A274731 257995068564,3361220228816,43792711784828,570555977597820, %U A274731 7433587136161392,96849404858071388,1261816522312628012 %N A274731 Number of 6Xn 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 A274731 Row 6 of A274728. %H A274731 R. H. Hardin, <a href="/A274731/b274731.txt">Table of n, a(n) for n = 1..210</a> %F A274731 Empirical: a(n) = 15*a(n-1) +a(n-2) -456*a(n-3) +1455*a(n-4) -196*a(n-5) -5263*a(n-6) +5258*a(n-7) +7193*a(n-8) -12179*a(n-9) -1317*a(n-10) +8177*a(n-11) -894*a(n-12) -2235*a(n-13) +104*a(n-14) +350*a(n-15) +27*a(n-16) -44*a(n-17) +5*a(n-18) for n>20 %e A274731 Some solutions for n=4 %e A274731 ..0..1..0..1. .0..1..0..2. .0..1..1..2. .0..1..0..2. .0..0..1..2 %e A274731 ..2..0..2..2. .1..0..2..0. .2..0..2..0. .2..0..1..0. .2..1..2..1 %e A274731 ..0..2..0..1. .2..1..0..1. .1..2..0..2. .0..1..0..1. .1..2..1..2 %e A274731 ..1..0..1..0. .0..0..1..0. .2..0..2..0. .1..0..2..0. .0..1..0..1 %e A274731 ..0..1..0..1. .2..1..2..2. .1..2..1..2. .0..2..0..2. .1..0..1..2 %e A274731 ..2..0..2..0. .1..2..1..0. .2..0..2..0. .1..0..2..0. .0..2..2..1 %Y A274731 Cf. A274728. %K A274731 nonn %O A274731 1,1 %A A274731 _R. H. Hardin_, Jul 03 2016