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Search: id:A107754
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| A107754 |
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Number of subsets of the n-th roots of unity that sum to 1. |
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+0
5
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| 1, 1, 1, 2, 1, 6, 1, 8, 4, 18, 1, 60, 1, 66, 20, 128, 1, 600, 1, 612, 68, 1026, 1, 6000, 16, 4098, 256, 8580, 1, 95226, 1, 32768
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OFFSET
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1,4
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FORMULA
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For prime p, a(p^i)=2^(p^(i-1)-1).
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MATHEMATICA
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<< DiscreteMath`Combinatorica`; f[n_] := Plus @@ Table[ Count[ KSubsets[ Range[n], k], q_List /; Chop[ -1 + Plus @@ (E^((2.*Pi*I*q)/n))] === 0], {k, 0, n}]; Table[ f[n], {n, 24}] (from Robert G. Wilson v (rgwv(AT)rgwv.com), Jun 03 2005)
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CROSSREFS
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Cf. A103314 (number of subsets of the n-th roots of unity summing to zero) and A108417 (number of subsets of the n-th roots of unity summing to the absolute value of 1.
Sequence in context: A050932 A166120 A007956 this_sequence A139625 A053785 A060173
Adjacent sequences: A107751 A107752 A107753 this_sequence A107755 A107756 A107757
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KEYWORD
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nonn
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AUTHOR
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T. D. Noe (noe(AT)sspectra.com), May 23 2005
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