Sister Beiter conjecture

In mathematics, the Sister Beiter conjecture is a conjecture about the size of coefficients of ternary cyclotomic polynomials (i.e. where the index is the product of three prime numbers). It is named after Marion Beiter, a Catholic nun who first proposed it in 1968.^[1]

For ${\displaystyle n\in \mathbb {N} _{>0}}$ the maximal coefficient (in absolute value) of the cyclotomic polynomial ${\displaystyle \Phi _{n}(x)}$ is denoted by ${\displaystyle A(n)}$.

Let ${\displaystyle 3\leq p\leq q\leq r}$ be three prime numbers. In this case the cyclotomic polynomial ${\displaystyle \Phi _{pqr}(x)}$ is called ternary. In 1895, A. S. Bang^[2] proved that ${\displaystyle A(pqr)\leq p-1}$. This implies the existence of ${\displaystyle M(p):=\max \limits _{p\leq q\leq r{\text{ prime}}}A(pqr)}$ such that ${\displaystyle 1\leq M(p)\leq p-1}$.

Sister Beiter conjectured^[1] in 1968 that ${\displaystyle M(p)\leq {\frac {p+1}{2}}}$. This was later disproved, but a corrected Sister Beiter conjecture was put forward as ${\displaystyle M(p)\leq {\frac {2}{3}}p}$.

A preprint^[3] from 2023 explains the history in detail and claims to prove this corrected conjecture. Explicitly it claims to prove $${\displaystyle M(p)\leq {\frac {2}{3}}p{\text{ and }}\lim \limits _{p\rightarrow \infty }{\frac {M(p)}{p}}={\frac {2}{3}}.}$$