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 A107848 #3 Mar 30 2012 17:22:40
%S A107848 2,4,4,8,8,24,16,48,40,144,64,336,128,864,416,1728,512,8304,1024,
%T A107848 10656,4032,31104,4096,116256,9248,186624,40000,374976,32768,3537024,
%U A107848 65536,2239488
%N A107848 Number of subsets of the n-th roots of unity summing to a real number.
%H A107848 T. D. Noe, <a href="http://www.sspectra.com/math/RootSums.html">Sums of Roots of Unity Plots</a>
%F A107848 For prime n, a(n)=2^((n+1)/2).
%t A107848 Needs["DiscreteMath`Combinatorica`"]; Table[Plus@@Table[Count[(KSubsets[Range[n], k]), q_List/;Im[Chop[Plus@@(E^(2.*Pi*I*q/n))]]==0], {k, 0, n}], {n, 20}]
%Y A107848 Cf. A103314 (number of subsets of the n-th roots of unity summing to zero).
%K A107848 nonn
%O A107848 1,1
%A A107848 _T. D. Noe_, May 25 2005