%I #7 Aug 22 2017 20:53:07
%S 0,0,0,24,240,1560,8400,40800,186480,818280,3498000,14674440,60780720,
%T 249393480,1016542560,4123132800,16664094960,67171179600,270232006800,
%U 1085569963080,4356217672800,17466683473800
%N Number of primitive (aperiodic) words of length n which contain exactly four different symbols.
%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)*A000919(n/d) where d|n.
%F Seems to be n * A056289.
%Y Cf. A000302, A000919, A054719.
%K nonn
%O 1,4
%A _Marks R. Nester_