TITLE: Cyclotomic polynomials with coefficients $0,\pm1$
QUESTION [23 upvotes]: Let me begin with what looks like a joke. According to a Bourbaki member, the following conversation occurred during a meeting dedicated to polishing the but-last version of an Algebra Bourbaki volume:
(a Bourbaki member) Why not state explicitly that the coefficients of cyclotomic polynomials are $0,\pm 1$ ?
(another member) Because it's false.
Here is what I am aware: if $n$ has at most two distinct odd prime factors, then the coefficients of  $\Phi_n(X)$ are $0,\pm1$ (Migotti, 1883). In other words, this holds true for $n=2^mp^kq^\ell$, where $p,q$ are primes. On the other hand, it is false for $n=105=3\cdot5\cdot7$, because the coefficient of $X^7$ (or of $X^{41}$ as well) is $-2$.

My question is whether there is a complete characterization of those $n$ for which the coefficients of  $\Phi_n(X)$ are $0,\pm1$ ? If not, are there other infinite lists of cyclotomic polynomials with this property?

REPLY [9 votes]: quid is correct; there are no complete characterizations of the known such numbers. In my work, now posted to the arXiv at http://arxiv.org/abs/1207.5811, I found the family he cites as well as the first fully general one for products of four primes, both listed in the abstract.