Presenter: Max Lewis (UQ)

A Carmichael number is a composite number $n$ that satisfies $a^{n-1} \equiv 1 \mod{n}$, for all integers $a$ such that $\gcd(a,\, n) = 1$. They are of interest in primality testing. Hsu defines Carmichael polynomials in $\mathbb{F}_q[x]$ for any prime power $q$, and shows that there are infinitely many such polynomials. We prove that for any $\mathbf{a},\, \mathbf{M} \in \mathbb{F}_q[x]$ where $\mathbf{M}$ is monic and $\gcd(\mathbf{a},\, \mathbf{M}) = 1$, there are infinitely many Carmichael polynomials that are congruent to $\mathbf{a}$ modulo $\mathbf{M}$. We also define analogues of Grau and Oller-Marc\'{e}n's $k$-Lehmer numbers and prove that for infinitely many $k$ there are Carmichael polynomials that are $k$-Lehmer but not $(k-1)$-Lehmer.

We present regular seminars on a range of pure mathematics interests. Students, staff and visitors to UQ are welcome to attend, and to suggest speakers and topics.

Seminars are held on Tuesdays from 3pm to 3.50pm in Room 67-442 of the Priestley Building (Building 67).

Talks comprise 45 minutes of speaking time plus five minutes for questions and discussion.

#### Information for speakers

Researchers in all pure mathematics fields attend our seminars, so please aim your presentation at a general mathematical audience.

Room 67-442 has a data projector and a whiteboard.

If you wish to use the data projector, contact us a few days in advance of your talk to avoid technical delays on the day - there's a tight turnaround with room bookings.