%I #14 Oct 01 2019 19:49:59

%S 0,0,0,0,0,1,1,7,10,43,65,219,350,1058,1701,4796,7770,21094,34105,

%T 90205,145749,379326,611501,1573205,2532530,6465123,10391735,26378849,

%U 42355950,107089814,171798901,433088656,694337225,1746623215,2798806984,7029320466,11259666950

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

%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]

%H Andrew Howroyd, <a href="/A056521/b056521.txt">Table of n, a(n) for n = 1..200</a>

%F a(n) = A056515(n) - A056514(n).

%F Moebius transform of A056510. - _T. D. Noe_, Oct 25 2006

%e For example, aaabbb is not a (finite) palindrome but it is a periodic palindrome. Permuting the symbols will not change the structure.

%Y Column 4 of A285037.

%Y Cf. A056483, A056510, A056514, A056515.

%K nonn

%O 1,8

%A _Marks R. Nester_

%E Corrected by _T. D. Noe_, Oct 25 2006

%E a(17)-a(30) from _Andrew Howroyd_, Apr 08 2017

%E Terms a(31) and beyond from _Andrew Howroyd_, Oct 01 2019