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A056278 Number of primitive (aperiodic) word structures of length n which contain exactly two different symbols. 4

%I

%S 0,1,3,6,15,27,63,120,252,495,1023,2010,4095,8127,16365,32640,65535,

%T 130788,262143,523770,1048509,2096127,4194303,8386440,16777200,

%U 33550335,67108608,134209530,268435455

%N Number of primitive (aperiodic) word structures of length n which contain exactly two different symbols.

%C Permuting the alphabet will not change a word structure. Thus aabc and bbca have the same structure. This is identical to A000740 for n>1.

%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)*A000225(n/d-1) where d|n and n>0.

%Y Apart from initial term, this is a duplicate of A000740.

%Y Column 2 of A137651.

%Y Cf. A056267.

%K nonn

%O 1,3

%A _Marks R. Nester_

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Last modified August 7 12:19 EDT 2020. Contains 336276 sequences. (Running on oeis4.)