OFFSET
1,2
COMMENTS
Mark m points around a horizontal disk with labels 0..m-1; place coins at positions k^3 mod m for k=0..m-1; sequence gives values of m for which the disk is not balanced.
LINKS
T. D. Noe, Table of n, a(n) for n = 1..1000
EXAMPLE
8 is in the sequence because 4 coins go at 0, and 1 each at 1, 3, 5, 7, so the disk is unbalanced in the direction of point 0.
12 is not in the sequence because there are 2 coins at 0, 4, 8 and 1 coin at 1, 3, 5, 7, 9, 11, so the disk is balanced.
MATHEMATICA
Select[Range[300], Sum[Exp[2 Pi*I*k^3/#], {k, 0, # - 1}] != 0 &] (* T. D. Noe, Jun 25 2012 *)
CROSSREFS
KEYWORD
nice,nonn,easy
AUTHOR
R. Lozyniak (11(AT)onna.com)
STATUS
approved