%I #9 Aug 22 2017 20:53:14

%S 0,1,1,2,3,4,7,10,14,21,31,42,63,91,123,184,255,371,511,750,1015,1519,

%T 2047,3030,4092,6111,8176,12222,16383,24486,32767,49024,65503,98175,

%U 131061,196308,262143,392959,524223,785910,1048575,1572256,2097151,3144702,4194162

%N Number of primitive (period n) periodic palindromic structures using exactly two different symbols.

%C For example, aaabbb is not a (finite) palindrome but it is a periodic palindrome. 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 A056513(n)-A000007(n-1).

%Y Column 2 of A285037.

%Y Cf. A056481.

%K nonn

%O 1,4

%A _Marks R. Nester_

%E a(17)-a(45) from _Andrew Howroyd_, Apr 08 2017