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A110981 a(n) = the number of aperiodic subsets S of the n-th roots of 1 with zero sum (i.e. there is no r different from 1 such that r*S=S). 5
1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 24, 0, 6, 0, 0, 0, 236, 0, 0, 0, 18, 0, 3768, 0, 0, 0, 0, 0, 20384, 0, 0, 0, 7188, 0, 227784, 0, 186, 480, 0, 0, 1732448, 0, 237600, 0, 630, 0, 16028160, 0, 306684, 0, 0, 0, 341521732, 0, 0, 4896, 0, 0, 1417919208 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,12

COMMENTS

We count these subsets only modulo rotations (multiplication by a nontrivial root of unity).

A103314(n) = a(n)*n + 2^n - A001037(n)*n. Note that as soon as a(n)=0, we have simply A103314(n) = 2^n - A001037(n)*n. This makes it especially interesting to study those n for which a(n)=0. Quite surprisingly, it appears that the sequence of such n coincides with A102466.

From Max Alekseyev, Jan 31 2008: (Start)

Every subset of the set U(n) = { 1=r^0, r^1, ..., r^(n-1) } of the n-th power roots of 1 (where r is a fixed primitive root) defines a binary word w of the length n where the j-th bit is 1 iff the root r^j is included in the subset.

If d is the period of w with respect to cyclic rotations (thus d|n) then the periodic part of w uniquely defines some binary Lyndon word of the length d (see A001037). In turn, each binary Lyndon word of the length d, where d<n and d|n, corresponds to d distinct zero-sum subsets of U(n).

The binary Lyndon words of the length n are different in this respect: only some of them correspond to n distinct zero-sum subsets of U(n) while the others do not correspond to such subsets at all. A110981(n) gives the number of binary Lyndon words of the length n that correspond to zero-sum subsets of U(n). (End)

LINKS

Max Alekseyev and M. F. Hasler, Table of n, a(n) for n = 1..164

FORMULA

a(n) = A001037(n) - A107847(n) ( = A001037(n) - (2^n - A103314(n))/n ). - M. F. Hasler, Jan 31 2008

CROSSREFS

Cf. A103314, A001037, A107847, A164896

Sequence in context: A123298 A189877 A189868 * A019261 A019222 A019141

Adjacent sequences:  A110978 A110979 A110980 * A110982 A110983 A110984

KEYWORD

nonn

AUTHOR

Max Alekseyev, Jan 20 2008

EXTENSIONS

Additional comments from M. F. Hasler, Jan 31 2008

STATUS

approved

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Last modified May 26 12:56 EDT 2017. Contains 287095 sequences.