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 A271029 #4 Mar 29 2016 07:43:20 %S A271029 0,20,294,3114,29120,256020,2173554,18060096,147976270,1201034302, %T A271029 9684108034,77719446198,621623562780,4959585660212,39496945637162, %U A271029 314112558505488,2495519478658458,19810840820555514,157179628657888198 %N A271029 Number of nXnXn triangular 0..3 arrays with some element less than a w, nw or ne neighbor exactly once. %C A271029 Column 3 of A271034. %H A271029 R. H. Hardin, <a href="/A271029/b271029.txt">Table of n, a(n) for n = 1..20</a> %e A271029 Some solutions for n=4 %e A271029 .....3........0........0........1........1........0........0........0 %e A271029 ....0.3......0.2......0.0......1.1......1.1......0.2......0.2......1.0 %e A271029 ...0.3.3....1.3.3....0.0.1....1.3.2....0.2.2....0.2.2....1.2.2....1.3.3 %e A271029 ..0.3.3.3..1.2.3.3..2.1.1.3..1.3.3.3..1.2.2.3..1.1.2.3..2.3.2.2..3.3.3.3 %Y A271029 Cf. A271034. %K A271029 nonn %O A271029 1,2 %A A271029 _R. H. Hardin_, Mar 29 2016