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 A255662 #7 Jan 21 2018 09:37:13 %S A255662 64,256,1016,3692,11752,33042,83752,195020,423460,867347,1690744, %T A255662 3158528,5686080,9908365,16774260,27673310,44603624,70391386, %U A255662 108974472,165764956,248107880,365856580,532088128,763986096,1083921900,1520770469 %N A255662 Number of length n+2 0..3 arrays with at most two downsteps in every n consecutive neighbor pairs. %C A255662 Row 2 of A255660. %H A255662 R. H. Hardin, <a href="/A255662/b255662.txt">Table of n, a(n) for n = 1..210</a> %F A255662 Empirical: a(n) = (1/39916800)*n^11 + (1/453600)*n^10 + (1/11520)*n^9 + (11/6048)*n^8 + (28751/1209600)*n^7 + (4303/21600)*n^6 + (789461/725760)*n^5 + (40955/18144)*n^4 + (164359/43200)*n^3 + (110513/6300)*n^2 + (44789/1540)*n + 10. %F A255662 Empirical g.f.: x*(64 - 512*x + 2168*x^2 - 5684*x^3 + 9864*x^4 - 11798*x^5 + 9944*x^6 - 5948*x^7 + 2500*x^8 - 711*x^9 + 124*x^10 - 10*x^11) / (1 - x)^12. - _Colin Barker_, Jan 21 2018 %e A255662 Some solutions for n=4: %e A255662 ..2....1....3....0....1....3....3....2....3....0....2....2....1....1....2....3 %e A255662 ..3....2....1....0....3....0....3....3....2....0....1....1....3....1....1....0 %e A255662 ..3....3....1....1....2....2....0....2....2....3....3....2....1....2....1....3 %e A255662 ..1....2....3....3....1....3....3....2....3....1....3....1....3....2....2....0 %e A255662 ..1....0....1....0....1....2....2....3....0....1....3....3....1....3....1....1 %e A255662 ..0....3....2....0....1....3....3....0....1....2....3....1....3....3....2....2 %Y A255662 Cf. A255660. %K A255662 nonn %O A255662 1,1 %A A255662 _R. H. Hardin_, Mar 01 2015