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A107848
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Number of subsets of the n-th roots of unity summing to a real number.
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1
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2, 4, 4, 8, 8, 24, 16, 48, 40, 144, 64, 336, 128, 864, 416, 1728, 512, 8304, 1024, 10656, 4032, 31104, 4096, 116256, 9248, 186624, 40000, 374976, 32768, 3537024, 65536, 2239488
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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LINKS
| T. D. Noe, Sums of Roots of Unity Plots
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FORMULA
| For prime n, a(n)=2^((n+1)/2).
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MATHEMATICA
| 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}]
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CROSSREFS
| Cf. A103314 (number of subsets of the n-th roots of unity summing to zero).
Sequence in context: A166632 A116596 A048656 * A188824 A181212 A029599
Adjacent sequences: A107845 A107846 A107847 * A107849 A107850 A107851
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KEYWORD
| nonn
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AUTHOR
| T. D. Noe (noe(AT)sspectra.com), May 25 2005
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