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%I #9 Aug 22 2017 20:53:11
%S 1,2,2,4,3,8,5,14,11,26,15,88,37,130,184,357,261,1346,805,3760,4434,
%T 9758,8385,47462,33781,108330,138767,408376,331185,2251816,1155735
%N Number of step cyclic shifted sequence structures using a maximum of two 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 Use de Bruijn's generalization of Polya's enumeration theorem as discussed in reference.
%F a(n) = A288627(n, 2) + 1. - _Andrew Howroyd_, Jun 13 2017
%Y Cf. A002729, A288627.
%K nonn
%O 1,2
%A _Marks R. Nester_