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