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 A056496 #16 Aug 22 2017 20:53:13
%S A056496 5,10,20,60,120,340,620,1800,3100,9240,15620,46440,78120,233740,
%T A056496 390480,1170000,1953120,5855900,9765620,29287440,48827480,146468740,
%U A056496 244140620,732373200,1220703000,3662031240
%N A056496 Number of primitive (period n) periodic palindromes using a maximum of five different symbols.
%C A056496 Number of aperiodic necklaces with five colors that are the same when turned over and hence have reflectional symmetry but no rotational symmetry. - _Herbert Kociemba_, Nov 29 2016
%D A056496 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]
%F A056496 a(n) = Sum_{d|n} mu(d)*A056487(n/d).
%F A056496 From _Herbert Kociemba_, Nov 29 2016: (Start)
%F A056496 More generally, gf(k) is the g.f. for the number of necklaces with reflectional symmetry but no rotational symmetry and beads of k colors.
%F A056496 gf(k): Sum_{n>=1} mu(n)*Sum_{i=0..2} binomial(k,i)x^(n*i)/(1-k*x^(2*n)). (End)
%e A056496 For example, aaabbb is not a (finite) palindrome but it is a periodic palindrome.
%t A056496 mx=40;gf[x_,k_]:=Sum[ MoebiusMu[n]*Sum[Binomial[k,i]x^(n i),{i,0,2}]/( 1-k x^(2n)),{n,mx}]; CoefficientList[Series[gf[x,5],{x,0,mx}],x] (* _Herbert Kociemba_, Nov 29 2016 *)
%Y A056496 Column 5 of A284856.
%Y A056496 Cf. A056461.
%K A056496 nonn
%O A056496 1,1
%A A056496 _Marks R. Nester_