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 A066518 #8 Jun 24 2014 01:08:18
%S A066518 0,0,0,-1,1,0,-2,2,0,-2,2,-1,-1,2,0,-2,0,2,-2,2,0,-4,4,-1,-1,2,-2,0,2,
%T A066518 0,-4,2,2,-2,2,0,-4,2,2,-3,3,-2,0,2,-2,0,0,2,-4,4,0,-6,6,0,-2,2,-2,-2,
%U A066518 2,1,-1,0,2,-2,2,-2,-4,6,0,-2,0,0,-2,4,0,-4,2,2,-2,0,2,-6,6,-1,-3,4,-4,2,2,0,-2,0,0,-4,6,0,-6,6,0,-2,0,0,-2
%N A066518 Anti-divisor class sums of n.
%C A066518 An anti-divisor of n is an integer d in [2,n-1] such that n == (d-1)/2, d/2, or (d+1)/2 (mod d), the class of d being -1, 0, or 1, respectively. The class sum of n is the sum of the classes of all of its anti-divisors.
%C A066518 See A066272 for definition of anti-divisor.
%H A066518 Jon Perry, <a href="http://www.users.globalnet.co.uk/~perry/maths/antidivisorother2.htm">Class sums</a>
%F A066518 f(n)=sum(ad class)
%e A066518 The ad's of 10 are 3, 4 and 7, with classes -1, 0 and -1, so f(10)=-2.
%t A066518 a[n_ ] := Sum[Which[Mod[n, d]==(d-1)/2, -1, Mod[n, d]==(d+1)/2, 1, True, 0], {d, 2, n-1}]
%Y A066518 Cf. A066519.
%K A066518 sign
%O A066518 1,7
%A A066518 _Jon Perry_, Jan 06 2002
%E A066518 Edited by _Dean Hickerson_, Jan 17 2002