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 A278663 #8 Nov 25 2016 20:18:48
%S A278663 0,0,3,3,6,3,14,3,24,11,54,3,148,3,318,59,834,3,2314,3,5952,323,16110,
%T A278663 3,45178,51,122646,2195,341820,3,962634,3,2690844,16115,7596486,363,
%U A278663 21568780,3,61171662,122651,174343026,3,498453878,3,1426419876,958819,4093181694,3,11770610128,315,33891550302
%N A278663 Number of periodic necklaces with n beads of 3 colors.
%F A278663 G.f.: k=3, Sum_{i>=1} (mu(i) - phi(i))*log(1 - k*x^i)/i.
%F A278663 a(n) = A001867(n) - A027376(n). - _Alois P. Heinz_, Nov 25 2016
%e A278663 Example: The 6 periodic necklaces with 4 beads and the colors A, B and C are AAAA, BBBB, CCCC, ABAB, ACAC and BCBC.
%t A278663 mx=40;f[x_,k_]:=Sum[(MoebiusMu[i]-EulerPhi[i])Log[1-k*x^i]/i,{i,1,mx}];CoefficientList[Series[f[x,3],{x,0,mx}],x]
%Y A278663 Cf. A001867, A027376, A066656 (2 colors).
%K A278663 nonn
%O A278663 0,3
%A A278663 _Herbert Kociemba_, Nov 25 2016