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 A250162 #9 Nov 12 2018 14:36:33 %S A250162 4,20,96,436,1880,7836,32032,129572,521256,2091052,8376368,33529908, %T A250162 134168632,536772668,2147287104,8589541444,34358952008,137437380684, %U A250162 549752668240,2199016964180,8796080439384,35184346923100,140737438023776 %N A250162 Number of length n+1 0..3 arrays with the sum of adjacent differences multiplied by some arrangement of +-1 equal to zero. %H A250162 R. H. Hardin, <a href="/A250162/b250162.txt">Table of n, a(n) for n = 1..59</a> %F A250162 Empirical: a(n) = 8*a(n-1) - 21*a(n-2) + 22*a(n-3) - 8*a(n-4). %F A250162 Conjectures from _Colin Barker_, Nov 12 2018: (Start) %F A250162 G.f.: 4*x*(1 - 3*x + 5*x^2) / ((1 - x)^2*(1 - 2*x)*(1 - 4*x)). %F A250162 a(n) = 2*(2 - 3*2^n + 4^n + 2*n). %F A250162 (End) %e A250162 Some solutions for n=6: %e A250162 ..1....3....3....2....3....2....2....2....2....1....1....2....1....0....2....1 %e A250162 ..1....0....2....3....3....0....2....2....2....1....0....0....1....2....0....0 %e A250162 ..0....3....1....3....3....2....3....3....2....3....3....0....1....2....3....2 %e A250162 ..3....1....0....0....0....3....1....1....2....2....3....2....3....3....0....1 %e A250162 ..0....2....3....3....3....2....3....2....1....0....1....3....3....1....2....2 %e A250162 ..1....1....0....1....3....0....2....0....0....1....2....2....0....3....0....2 %e A250162 ..3....3....1....2....3....2....2....0....2....3....1....0....1....2....2....3 %Y A250162 Column 3 of A250167. %K A250162 nonn %O A250162 1,1 %A A250162 _R. H. Hardin_, Nov 13 2014