%N Number of primitive (period n) periodic palindromic structures using a maximum of six different symbols.
%C For example, aaabbb is not a (finite) palindrome but it is a periodic palindrome. Permuting the symbols will not change the structure.
%D M. R. Nester (1999). Mathematical investigations of some plant interaction designs. PhD Thesis. University of Queensland, Brisbane, Australia. [See A056391 for pdf file of Chap. 2]
%F Sum mu(d)*A056507(n/d) where d|n.
%Y Cf. A056480.
%A _Marks R. Nester_
%E Corrected by _T. D. Noe_, Oct 25 2006