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%I #6 Aug 22 2017 20:53:12
%S 1,1,2,5,6,29,28,142,242,1222,1664,15935,18198,134452,376424,1415060,
%T 2634596,26534337,33499358,287001476,727425470,3332039278,5794658930,
%U 61120838930,93825569002,601444720052
%N Number of primitive (period n) step cyclic shifted sequence structures using a maximum of four different symbols.
%C See A056371 for an explanation of step shifts. Under step cyclic shifts, abcde, bdace, bcdea, cdeab and daceb etc. are equivalent. 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)*A056431(n/d) where d|n.
%Y Cf. A056421.
%K nonn
%O 1,3
%A _Marks R. Nester_