Search: id:A107848
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%I A107848
%S A107848 2,4,4,8,8,24,16,48,40,144,64,336,128,864,416,1728,512,8304,1024,10656,
%T A107848 4032,31104,4096,116256,9248,186624,40000,374976,32768,3537024,65536,
%U A107848 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).
%Y A107848 Sequence in context: A166632 A116596 A048656 this_sequence A029599 A076466 
               A073117
%Y A107848 Adjacent sequences: A107845 A107846 A107847 this_sequence A107849 A107850 
               A107851
%K A107848 nonn
%O A107848 1,1
%A A107848 T. D. Noe (noe(AT)sspectra.com), May 25 2005

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