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 A212938 #13 Jul 21 2018 15:52:27 %S A212938 1,181,9019,331489,10669771,320396041,9245913139,260489615329, %T A212938 7229878904251,198760197641401,5430623746397059,147781972534146769, %U A212938 4010919223287633931,108669462396348197161,2940820425317878781779 %N A212938 Number of n X 3 0..2 arrays with no column j greater than or equal to than column j-1 in all rows. %C A212938 Column 3 of A212943. %H A212938 R. H. Hardin, <a href="/A212938/b212938.txt">Table of n, a(n) for n = 1..210</a> %F A212938 Empirical: a(n) = 55*a(n-1) - 936*a(n-2) + 4860*a(n-3). %F A212938 a(n) = 10^n - 2*18^n + 27^n. - _Vaclav Kotesovec_, May 31 2012 %F A212938 Empirical g.f.: x*(1 + 126*x) / ((1 - 10*x)*(1 - 18*x)*(1 - 27*x)). - _Colin Barker_, Jul 21 2018 %e A212938 Some solutions for n=4: %e A212938 ..2..1..2....2..2..0....0..0..0....1..0..1....0..1..1....0..1..2....1..1..1 %e A212938 ..0..2..2....2..1..1....2..1..0....2..0..2....2..2..2....0..1..0....2..1..1 %e A212938 ..2..0..0....1..1..0....0..2..0....0..2..2....1..2..2....0..2..1....1..1..1 %e A212938 ..2..1..0....0..1..2....0..0..2....2..1..0....2..1..0....1..0..0....0..1..0 %Y A212938 Cf. A212943. %K A212938 nonn %O A212938 1,2 %A A212938 _R. H. Hardin_, May 31 2012