%N Number of primitive (aperiodic) reversible strings with n beads using exactly four different colors.
%C A string and its reverse are considered to be equivalent.
%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)*A056311(n/d) where d|n.
%Y Cf. A056315.
%A _Marks R. Nester_