%I #9 Aug 08 2015 07:38:53
%S 4,9,21,51,127,324,844,2243,6073,16737,46905,133556,386062,1132107,
%T 3365627,10137559,30920943,95457178,298128278,941574417,3006040523,
%U 9697677885,31602993021,104001763258,345524136076,1158570129917
%N Number of length n+2 0..n arrays with no three unequal elements in a row and new values 0..n introduced in 0..n order.
%C Diagonal of A243641.
%H R. H. Hardin, <a href="/A243634/b243634.txt">Table of n, a(n) for n = 1..209</a>
%e Some solutions for n=6
%e ..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
%e ..1....1....0....1....1....1....1....1....0....1....0....1....1....0....1....0
%e ..1....0....1....0....1....1....1....1....1....0....0....0....1....1....0....1
%e ..1....1....1....0....2....0....2....1....1....1....1....0....0....0....1....1
%e ..2....1....0....0....1....1....2....1....1....0....1....1....0....0....1....1
%e ..2....2....0....0....1....0....1....2....2....0....1....1....2....1....2....1
%e ..2....1....2....1....3....0....1....2....2....2....1....1....2....1....2....0
%e ..2....1....2....0....3....1....1....1....2....0....0....0....1....0....1....0
%Y Cf. A247100.
%K nonn
%O 1,1
%A _R. H. Hardin_, Jun 08 2014