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A107848 Number of subsets of the n-th roots of unity summing to a real number. 3
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; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..32.

T. D. Noe, Sums of Roots of Unity Plots

FORMULA

For prime n, a(n)=2^((n+1)/2).

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}]

CROSSREFS

Cf. A103314 (number of subsets of the n-th roots of unity summing to zero).

Sequence in context: A116596 A248692 A048656 * A285273 A188824 A181212

Adjacent sequences:  A107845 A107846 A107847 * A107849 A107850 A107851

KEYWORD

nonn

AUTHOR

T. D. Noe, May 25 2005

STATUS

approved

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Last modified November 27 01:16 EST 2021. Contains 349344 sequences. (Running on oeis4.)