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A107754
Number of subsets of the n-th roots of unity that sum to 1.
7
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
OFFSET
1,4
FORMULA
For prime p, a(p^i) = 2^(p^(i-1)-1).
MATHEMATICA
<< 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}] (* Robert G. Wilson v, Jun 03 2005 *)
CROSSREFS
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: A364829 A264859 A007956 * A181569 A274085 A302129
KEYWORD
nonn,more
AUTHOR
T. D. Noe, May 23 2005
STATUS
approved