%N Number of primitive (aperiodic) reversible string structures with n beads using exactly four different colors.
%C A string and its reverse are considered to be equivalent. Permuting the colors 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]
%Y Column 4 of A276544.
%Y Cf. A056320.
%A _Marks R. Nester_