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%I #8 Oct 15 2017 08:47:08
%S 1,2,4,11,18,117,162,1205,3621,29271,68086,1069614,2305158,31825670,
%T 172974370,1311400891,5179123522,113680235941,324041807958,
%U 6466011855715,39572612670818,450671611457619,2006909406239780,55745145216877102,231929517217884081
%N Number of step shifted (decimated) sequence structures of length n using an infinite alphabet.
%C See A056371 for an explanation of step shifts. 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]
%o (PARI) \\ see A056391 for Polya enumeration functions
%o a(n) = NonequivalentStructs(StepShiftPerms(n), n); \\ _Andrew Howroyd_, Oct 14 2017
%Y Row sums of A288620.
%Y Cf. A056391, A056371, A288628.
%K nonn
%O 1,2
%A _Andrew Howroyd_, Jun 11 2017