This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A056517 #11 Oct 01 2019 19:49:17
%S A056517 1,1,1,1,3,4,10,14,36,50,138,202,561,875,2571,4105,12548,20647,65456,
%T A056517 109298,356466,601476,2005341,3403126,11522216,19628059,67182654,
%U A056517 114700263,395494722,676207627,2343260789,4010090462,13942474064,23874361996,83192218842,142508723632
%N A056517 Number of primitive (period n) periodic palindromic structures using a maximum of six different symbols.
%C A056517 For example, aaabbb is not a (finite) palindrome but it is a periodic palindrome.
%C A056517 Permuting the symbols will not change the structure.
%D A056517 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 A056517 Andrew Howroyd, <a href="/A056517/b056517.txt">Table of n, a(n) for n = 0..200</a>
%F A056517 a(n) = Sum_{d|n} mu(d)*A056507(n/d) for n > 0.
%F A056517 a(n) = Sum_{k=1..6} A285037(n, k) for n > 0. - _Andrew Howroyd_, Oct 01 2019
%Y A056517 Cf. A056480, A056507, A285037.
%K A056517 nonn
%O A056517 0,5
%A A056517 _Marks R. Nester_
%E A056517 Corrected by _T. D. Noe_, Oct 25 2006
%E A056517 a(0)=1 prepended and terms a(16) and beyond from _Andrew Howroyd_, Oct 01 2019