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 A056499 #10 Sep 29 2019 11:39:12
%S A056499 0,0,0,3,6,21,36,90,150,339,540,1149,1806,3765,5790,11880,18150,36894,
%T A056499 55980,113145,170970,344541,519156,1043190,1569744,3149979,4733670,
%U A056499 9488409,14250606,28544205,42850116,85786560,128746410,257672355,386634018,773623116,1160688606
%N A056499 Number of primitive (period n) periodic palindromes using exactly three different symbols.
%C A056499 For example, aaabbb is not a (finite) palindrome but it is a periodic palindrome.
%D A056499 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 A056499 Andrew Howroyd, <a href="/A056499/b056499.txt">Table of n, a(n) for n = 1..200</a>
%F A056499 a(n) = Sum_{d|n} mu(d)*A056489(n/d).
%Y A056499 Column 3 of A327878.
%Y A056499 Cf. A056464, A056489.
%K A056499 nonn
%O A056499 1,4
%A A056499 _Marks R. Nester_
%E A056499 Terms a(32) and beyond from _Andrew Howroyd_, Sep 28 2019