OFFSET
1,2
COMMENTS
A055034(n) is the degree delta(n) of the minimal polynomial of the algebraic number rho(n):=2*cos(pi/n), n>=1, whose coefficients are shown in A187360. It is also the order of multiplicative abelian group Modd n (for multiplication Modd n see a comment on A203571). This is the Galois group Gal(Q(rho(n))/Q). If the number of abelian groups of order delta(n) is 1 then this group is necessarily cyclic.
Because A000688 is 1 exactly for the squarefree numbers A005117, the set of a(n) values of the present sequence is a (proper) subset of A206551. Hence it is immediately clear that the multiplicative group Modd a(n) is cyclic, but there are other cyclic Modd n groups, e.g., for n = 8, 10, 15, 16, 17, 19, 26, 27, 32, 34, 35, 37, 38, 39, 41,...
EXAMPLE
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wolfdieter Lang, Apr 11 2012
STATUS
approved