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 A255102 #8 Jan 24 2018 10:55:24 %S A255102 66,168,441,1137,2907,7498,19338,49698,127871,329325,847491,2180700, %T A255102 5613144,14447250,37180603,95692059,246288681,633868172,1631378124, %U A255102 4198705332,10806224445,27811942767,71579710341,184225016494 %N A255102 Number of length n+3 0..2 arrays with at most one downstep in every 3 consecutive neighbor pairs. %C A255102 Column 3 of A255107. %H A255102 R. H. Hardin, <a href="/A255102/b255102.txt">Table of n, a(n) for n = 1..210</a> %F A255102 Empirical: a(n) = 3*a(n-1) -3*a(n-2) +8*a(n-3) -9*a(n-4) +3*a(n-5) -a(n-6). %F A255102 Empirical g.f.: x*(66 - 30*x + 135*x^2 - 210*x^3 + 69*x^4 - 26*x^5) / ((1 - x)*(1 - 2*x + x^2 - 7*x^3 + 2*x^4 - x^5)). - _Colin Barker_, Jan 24 2018 %e A255102 Some solutions for n=4: %e A255102 ..0....2....0....2....2....1....0....0....0....2....2....0....0....0....0....2 %e A255102 ..1....1....2....1....0....1....2....1....2....2....0....0....1....1....0....0 %e A255102 ..0....1....0....1....1....1....0....0....2....2....0....0....1....2....0....0 %e A255102 ..2....1....0....1....2....2....1....0....2....2....1....1....0....0....1....1 %e A255102 ..2....2....1....1....1....2....1....2....2....2....1....2....0....0....2....0 %e A255102 ..1....1....1....1....1....0....0....2....2....2....1....1....0....2....1....0 %e A255102 ..2....2....0....0....2....2....1....1....1....1....1....1....1....2....2....1 %Y A255102 Cf. A255107. %K A255102 nonn %O A255102 1,1 %A A255102 _R. H. Hardin_, Feb 14 2015