Question on cyclotomic polynomials

[Edwin Clark]

On Fri, 19 May 2006 franktaw at netscape.net wrote:

> Somebody on this list must know the answer to this question.
>  
> It is well known that the cyclomatic polynomial Phi_n of order n can have a coefficient with absolute value greater than 1 only if n has at least 3 distinct prime factors.  The question is, is this if and only if?
>  

No, if n = 2*3*5 or 3*7*11 then Phi_n(x) has coefficients 0,1,-1 only. 

Maple calculates Phi_n(x) for such values of n pretty fast.