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 A056515 #10 Oct 01 2019 19:05:31
%S A056515 1,1,1,1,3,4,10,14,35,49,127,186,463,714,1799,2789,6996,11050,27685,
%T A056515 43946,109925,175259,438495,700074,1750445,2798246,6996927,11188856,
%U A056515 27973533,44747434,111873782,178973354,447438656,715860463,1789673215,2863377048,7158463662
%N A056515 Number of primitive (period n) periodic palindromic structures using a maximum of four different symbols.
%C A056515 For example, aaabbb is not a (finite) palindrome but it is a periodic palindrome. Permuting the symbols will not change the structure.
%D A056515 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 A056515 Andrew Howroyd, <a href="/A056515/b056515.txt">Table of n, a(n) for n = 0..200</a>
%F A056515 a(n) = Sum_{d|n} mu(d)*A056505(n/d) for n > 0.
%F A056515 Moebius transform of A056505.
%F A056515 a(n) = Sum_{k=1..4} A285037(n, k) for n > 0. - _Andrew Howroyd_, Oct 01 2019
%Y A056515 Cf. A056478, A056505, A285037.
%K A056515 nonn
%O A056515 0,5
%A A056515 _Marks R. Nester_
%E A056515 a(0)=1 prepended and terms a(17) and beyond from _Andrew Howroyd_, Oct 01 2019