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%I A056521 #14 Oct 01 2019 19:49:59
%S A056521 0,0,0,0,0,1,1,7,10,43,65,219,350,1058,1701,4796,7770,21094,34105,
%T A056521 90205,145749,379326,611501,1573205,2532530,6465123,10391735,26378849,
%U A056521 42355950,107089814,171798901,433088656,694337225,1746623215,2798806984,7029320466,11259666950
%N A056521 Number of primitive (period n) periodic palindromic structures using exactly four different symbols.
%D A056521 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 A056521 Andrew Howroyd, <a href="/A056521/b056521.txt">Table of n, a(n) for n = 1..200</a>
%F A056521 a(n) = A056515(n) - A056514(n).
%F A056521 Moebius transform of A056510. - _T. D. Noe_, Oct 25 2006
%e A056521 For example, aaabbb is not a (finite) palindrome but it is a periodic palindrome. Permuting the symbols will not change the structure.
%Y A056521 Column 4 of A285037.
%Y A056521 Cf. A056483, A056510, A056514, A056515.
%K A056521 nonn
%O A056521 1,8
%A A056521 _Marks R. Nester_
%E A056521 Corrected by _T. D. Noe_, Oct 25 2006
%E A056521 a(17)-a(30) from _Andrew Howroyd_, Apr 08 2017
%E A056521 Terms a(31) and beyond from _Andrew Howroyd_, Oct 01 2019

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