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Number of primitive (period n) periodic palindromes using exactly three different symbols.
2

%I #10 Sep 29 2019 11:39:12

%S 0,0,0,3,6,21,36,90,150,339,540,1149,1806,3765,5790,11880,18150,36894,

%T 55980,113145,170970,344541,519156,1043190,1569744,3149979,4733670,

%U 9488409,14250606,28544205,42850116,85786560,128746410,257672355,386634018,773623116,1160688606

%N Number of primitive (period n) periodic palindromes using exactly three different symbols.

%C For example, aaabbb is not a (finite) palindrome but it is a periodic palindrome.

%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="/A056499/b056499.txt">Table of n, a(n) for n = 1..200</a>

%F a(n) = Sum_{d|n} mu(d)*A056489(n/d).

%Y Column 3 of A327878.

%Y Cf. A056464, A056489.

%K nonn

%O 1,4

%A _Marks R. Nester_

%E Terms a(32) and beyond from _Andrew Howroyd_, Sep 28 2019