%I
%S 6561,19683,59049,152106,322078,602886,1047141,1706242,2653107,
%T 3977859,5790140,8221629,11428785,15595837,20938044,27705249,36185752,
%U 46710528,59657817,75458114,94599588,117633960,145182871,177944772,216702369
%N Number of length n+7 0..2 arrays with at most two downsteps in every n consecutive neighbor pairs
%C Row 7 of A255622
%H R. H. Hardin, <a href="/A255629/b255629.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = (1/40320)*n^8 + (23/10080)*n^7 + (239/2880)*n^6 + (1541/144)*n^5 + (920887/5760)*n^4 + (442121/1440)*n^3 + (42883817/3360)*n^2  (2307073/56)*n + 29319 for n>5
%e Some solutions for n=4
%e ..1....2....0....2....1....1....2....2....2....1....0....2....0....0....0....1
%e ..1....0....1....0....0....0....0....0....0....0....0....0....2....1....0....1
%e ..1....0....2....0....1....0....0....1....0....1....1....0....0....0....0....1
%e ..2....0....1....2....2....2....1....1....0....2....2....1....2....2....1....1
%e ..0....1....1....2....1....2....2....1....0....1....1....2....0....1....1....1
%e ..2....2....2....0....2....0....0....1....0....0....0....0....2....2....0....1
%e ..1....1....0....0....0....2....0....2....2....2....2....0....0....2....2....2
%e ..2....1....2....1....0....0....2....0....0....2....2....0....0....2....2....0
%e ..2....0....1....1....0....1....0....1....2....2....0....0....1....2....2....2
%e ..2....2....2....2....0....1....0....1....2....2....1....0....2....0....2....2
%e ..1....0....1....0....0....0....1....1....0....0....0....1....2....2....1....2
%Y Cf. A255622
%K nonn
%O 1,1
%A _R. H. Hardin_, Feb 28 2015
