 # Celebratio Mathematica

## Paul T. Bateman

### Work on coefficients ofcylotomic polynomials

#### by A. J. Hildebrand

Let $\Phi_n(z)=\prod_{\substack{r=1\\ (r,n)=1}}^{n}\!\! \left(1-e^{2\pi i r/n}\right)=\sum_{m=0}^{\phi(n)}a(m,n)z^m$ be the $n$-th cyc­lo­tom­ic poly­no­mi­al. In 1949, in his first pub­lished pa­per, Paul Bate­man  proved the in­equal­ity \begin{equation} \max_{m}|a(m,n)|\le \exp\Big(\tfrac{1}{2}d(n)\log n\Big), \label{one} \end{equation} where $d(n)$ is the di­visor func­tion, and de­duced from this the bound \begin{equation} \log \max_{m}|a(m,n)|\le \exp\Bigl(\bigl(1+o(1)\bigr)\frac{(\log 2)(\log n)}{\log\log n}\Bigr). \label{two} \end{equation} Bate­man’s proof of \eqref{one} and \eqref{two} takes just over one page, and is a mod­el of sim­pli­city and el­eg­ance. His work was mo­tiv­ated by a 1946 pa­per of Paul Er­dős [e1], in which Er­dős gave a lower bound for $\max_m|a(m,n)|$ among oth­er res­ults and con­jec­tures.

The pa­pers by Er­dős and Bate­man gave im­petus to sig­ni­fic­ant fur­ther work on the coef­fi­cients of cyc­lo­tom­ic poly­no­mi­als. We men­tion here some of the key res­ults that have been ob­tained dur­ing the past few dec­ades. In 1974, Robert Vaughan [e2] showed that the up­per bound \eqref{two} is best pos­sible, in the sense that an in­equal­ity in the oth­er dir­ec­tion holds for in­fin­itely many $n$. In 1984, Bate­man, Carl Pom­er­ance, and Vaughan  gave up­per and lower bounds for $\max_m|a(m,n)|$ in terms of the num­ber of prime factors of $n$. In 1990, Helmut Maier [e3] proved a long-stand­ing con­jec­ture on the “typ­ic­al” size of the max­im­al coef­fi­cient $\max_m|a(m,n)|$ by show­ing that, for “al­most all” $n$, one has $\max_{m}|a(m,n)|\ge n^{\epsilon(n)}$ for any giv­en func­tion $\epsilon(n)\to0$. In 1993, Gen­nady Bach­man [e4] con­sidered the size of the coef­fi­cient $a(m,n)$ when $m$ is fixed and $n$ var­ies, and he ob­tained an asymp­tot­ic for­mula for $\log \max_n|a(m,n)|$ as $m\to\infty$.

The above pa­pers settle some of the key prob­lems in this area, but many oth­er open ques­tions re­main, and the sub­ject con­tin­ues to at­tract the at­ten­tion of re­search­ers. Of the four­teen pa­pers that ref­er­ence the 1984 pa­per  of Bate­man, Pom­er­ance, and Vaughan, ac­cord­ing to the Math­S­ciNet data­base, five have been pub­lished since 2010.

### Works

P. T. Bate­man: “On the rep­res­ent­a­tions of a num­ber as the sum of three squares,” Trans. Am. Math. Soc. 71 : 1 (1951), pp. 70–​101. This is Bate­man’s 1946 PhD thes­is. MR 0042438 Zbl 0043.​04603 article

P. T. Bate­man, C. Pom­er­ance, and R. C. Vaughan: “On the size of the coef­fi­cients of the cyc­lo­tom­ic poly­no­mi­al,” pp. 171–​202 in Top­ics in clas­sic­al num­ber the­ory (Bud­apest, 20–25 Ju­ly 1981), vol. I. Edi­ted by G. Halász. Col­loquia Math­em­at­ica So­ci­e­tatis János Bolyai 34. North-Hol­land (Am­s­ter­dam), 1984. Note that an art­icle with the same title had been pub­lished by Bate­man alone in 1982. MR 781138 Zbl 0547.​10010 incollection