%I #9 Dec 12 2015 01:48:14
%S 4,12,24,72,120,408,840,2448,5760,15960,39864,108024,275184,728784,
%T 1895760,4998528,13033560,34250904,89602632,235157640,615871032
%N Number of length-n 0..3 arrays connected end-around, with no sequence of L<n elements immediately followed by itself (periodic "squarefree").
%C Column 3 of A215228.
%e Some solutions for n=8:
%e ..0....1....2....2....0....3....2....1....0....1....1....0....1....0....0....3
%e ..3....3....3....3....1....0....3....0....2....2....0....3....3....2....3....1
%e ..1....0....1....2....2....2....0....3....1....0....2....1....1....1....2....0
%e ..2....2....0....1....3....1....2....0....3....3....3....2....2....3....1....1
%e ..0....3....3....2....0....2....1....1....0....1....2....0....0....1....3....3
%e ..2....0....0....0....3....3....0....3....3....3....1....3....1....0....1....0
%e ..1....3....1....2....1....2....3....0....1....0....0....0....0....3....0....3
%e ..2....2....3....1....2....0....1....2....3....2....3....1....2....2....2....2
%K nonn,more
%O 1,1
%A _R. H. Hardin_, Aug 06 2012