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%I #15 Jun 29 2018 10:23:00
%S 0,1,2,4,9,16,35,66,133,261,527,1032,2079,4123,8244,16440,32895,65639,
%T 131327,262380,524762,1049071,2098175,4195230,8390646,16779231,
%U 33558392,67112892,134225919,268443306
%N Number of primitive (aperiodic) reversible string structures with n beads using exactly two different colors.
%C A string and its reverse are considered to be equivalent. Permuting the colors will not change the structure. Identical to A056331 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 a(n) = A056331(n) - A063524(n).
%t a[1] = 0;
%t a[n_] := DivisorSum[n, MoebiusMu[#] (2^(n/#-2) + 2^(Floor[n/#/2]-1))&];
%t Array[a, 30] (* _Jean-François Alcover_, Jun 29 2018 *)
%Y Column 2 of A276544.
%Y Cf. A056318, A056331, A063524.
%K nonn
%O 1,3
%A _Marks R. Nester_