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 A056497 #16 Aug 22 2017 20:53:13
%S A056497 6,15,30,105,210,705,1290,4410,7740,26985,46650,162435,279930,978465,
%T A056497 1679370,5874120,10077690,35263440,60466170,211604295,362795730,
%U A056497 1269743025,2176782330,7618570470,13060693800
%N A056497 Number of primitive (period n) periodic palindromes using a maximum of six different symbols.
%C A056497 Number of aperiodic necklaces with six colors that are the same when turned over and hence have reflectional symmetry but no rotational symmetry. - _Herbert Kociemba_, Nov 29 2016
%D A056497 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 A056497 a(n) = Sum_{d|n} mu(d)*A056488(n/d).
%F A056497 From _Herbert Kociemba_, Nov 29 2016: (Start)
%F A056497 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 A056497 gf(k): Sum_{n>=1} mu(n)*Sum_{i=0..2} binomial(k,i)x^(n*i)/(1-k*x^(2*n)). (End)
%e A056497 For example, aaabbb is not a (finite) palindrome but it is a periodic palindrome.
%t A056497 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,6],{x,0,mx}],x] (* _Herbert Kociemba_, Nov 29 2016 *)
%Y A056497 Column 6 of A284856.
%Y A056497 Cf. A056462.
%K A056497 nonn
%O A056497 1,1
%A A056497 _Marks R. Nester_