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 A255109 #10 Jan 25 2018 02:52:21 %S A255109 27,75,168,331,597,1008,1616,2484,3687,5313,7464,10257,13825,18318, %T A255109 23904,30770,39123,49191,61224,75495,92301,111964,134832,161280, %U A255109 191711,226557,266280,311373,362361,419802,484288,556446,636939,726467,825768,935619 %N A255109 Number of length n+2 0..2 arrays with at most one downstep in every n consecutive neighbor pairs. %C A255109 Row 2 of A255107. %H A255109 R. H. Hardin, <a href="/A255109/b255109.txt">Table of n, a(n) for n = 1..210</a> %F A255109 Empirical: a(n) = (1/120)*n^5 + (5/24)*n^4 + (37/24)*n^3 + (175/24)*n^2 + (239/20)*n + 6. %F A255109 Empirical g.f.: x*(3 - 3*x + x^2)*(9 - 20*x + 18*x^2 - 6*x^3) / (1 - x)^6. - _Colin Barker_, Jan 24 2018 %e A255109 Some solutions for n=4: %e A255109 0 2 2 0 2 2 1 0 0 1 1 1 1 2 2 2 %e A255109 0 2 0 1 0 2 1 0 2 1 0 1 1 1 0 2 %e A255109 0 1 2 0 1 2 1 0 0 2 0 2 0 1 1 0 %e A255109 1 1 2 1 2 0 0 2 0 1 0 2 0 1 1 0 %e A255109 0 1 2 2 2 2 1 2 0 1 2 1 1 1 2 0 %e A255109 1 1 2 2 2 2 2 2 1 2 1 2 1 2 2 1 %Y A255109 Cf. A255107. %K A255109 nonn %O A255109 1,1 %A A255109 _R. H. Hardin_, Feb 14 2015