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 A274891 #6 Jul 10 2016 20:05:36 %S A274891 4,36,37,104,275,753,2049,5602,15305,41866,114475,313122,856462, %T A274891 2342559,6407780,17526908,47941766,131135884,358697083,981151642, %U A274891 2683758871,7340930445,20079778989,54924550811,150236085835,410943350656 %N A274891 Number of nX4 0..2 arrays with no element equal to any value at offset (0,-1) (-1,-1) or (-2,0) and new values introduced in order 0..2. %C A274891 Column 4 of A274895. %H A274891 R. H. Hardin, <a href="/A274891/b274891.txt">Table of n, a(n) for n = 1..210</a> %F A274891 Empirical: a(n) = a(n-1) +8*a(n-2) -28*a(n-4) -9*a(n-5) +55*a(n-6) +16*a(n-7) -70*a(n-8) -9*a(n-9) +56*a(n-10) -28*a(n-12) +a(n-13) +8*a(n-14) -a(n-16) for n>18 %e A274891 Some solutions for n=4 %e A274891 ..0..1..2..0. .0..1..0..1. .0..1..0..2. .0..1..2..1. .0..1..2..0 %e A274891 ..1..2..0..1. .2..1..2..1. .2..1..2..1. .1..2..0..1. .1..2..0..1 %e A274891 ..2..0..1..2. .1..0..2..0. .1..0..2..0. .2..0..1..2. .2..0..1..2 %e A274891 ..0..1..2..0. .1..2..1..0. .1..0..1..0. .0..1..2..0. .2..0..1..0 %Y A274891 Cf. A274895. %K A274891 nonn %O A274891 1,1 %A A274891 _R. H. Hardin_, Jul 10 2016