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 A208593 #12 Nov 01 2017 12:25:13
%S A208593 1,5,21,125,791,5457,39019,288317,2178929,16773395,131034839,
%T A208593 1036252649,8279446917,66733111919,541954722471,4430427981533,
%U A208593 36428763143945,301074015186469,2499725665085301,20840038803521835,174388665638906551,1464205768804076875
%N A208593 Number of n-bead necklaces labeled with numbers -4..4 not allowing reversal, with sum zero.
%H A208593 Andrew Howroyd, <a href="/A208593/b208593.txt">Table of n, a(n) for n = 1..100</a>
%F A208593 a(n) = (1/n) * Sum_{d | n} totient(n/d) * A025014(d). - _Andrew Howroyd_, Mar 02 2017
%e A208593 All solutions for n=3:
%e A208593 .-4...-2...-2...-3...-1...-3...-2...-3...-3...-4....0...-3...-2...-4...-1...-4
%e A208593 ..2...-1....2....1....1....2....3...-1....3....1....0....0....0....0....0....3
%e A208593 ..2....3....0....2....0....1...-1....4....0....3....0....3....2....4....1....1
%e A208593 ..
%e A208593 .-1...-4...-3...-2...-2
%e A208593 .-1....4....4....1...-2
%e A208593 ..2....0...-1....1....4
%t A208593 comps[r_, m_, k_] := Sum[(-1)^i*Binomial[r - 1 - i*m, k - 1]*Binomial[k, i], {i, 0, Floor[(r - k)/m]}]; a[n_Integer, k_] := DivisorSum[n, EulerPhi[n/#] comps[#*(k + 1), 2 k + 1, #] &]/n; a[n_] = a[n, 4]; Array[a, 22] (* _Jean-François Alcover_, Nov 01 2017, after _Andrew Howroyd_ *)
%Y A208593 Column 4 of A208597.
%K A208593 nonn
%O A208593 1,2
%A A208593 _R. H. Hardin_, Feb 29 2012
%E A208593 a(16)-a(22) from _Andrew Howroyd_, Mar 02 2017