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%I #22 Oct 01 2019 18:28:24
%S 0,0,0,1,1,5,6,19,25,64,90,208,301,656,966,2035,3025,6250,9330,19035,
%T 28501,57740,86526,174436,261625,525994,788970,1583119,2375101,
%U 4760516,7141686,14303011,21457825,42954850,64439010,128953341,193448101,387046700,580606446,1161504423
%N Number of periodic palindromic structures of length n using exactly three 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="/A056509/b056509.txt">Table of n, a(n) for n = 1..200</a>
%F a(n) = A056504(n) - A056503(n).
%F Inverse Moebius transform of A056519. - _Andrew Howroyd_, Oct 01 2019
%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 3 of A285012.
%Y Cf. A000392, A056503, A056504, A056519.
%K nonn
%O 1,6
%A _Marks R. Nester_
%E a(17)-a(35) from _Andrew Howroyd_, Apr 07 2017
%E Terms a(36) and beyond from _Andrew Howroyd_, Oct 01 2019
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