arXiv subjects

Andrew Shallue

Publications and source records attributed to Andrew Shallue.

8 recordsLinked to original sources

arXiv2025

Algorithms for Carmichael numbers

Our primary concern is the computational complexity of algorithms that find all Carmichael numbers less than some specified bound $B$. We have three related results. First, we show CARMICHAELS is in $\textbf{P}$, where only the run-time is conditioned on the ERH. Second, we state a heuristically optimal tabulation algorithm, which is the first asymptotic improvement to tabulation algorithms in the $50$ years since Swift first described the prime-by-prime approach. Third, we implemented a related algorithm that tabulated $100$ times further while only doing about $5$ times the work of the prior tabulation. We found $308,279,939$ Carmichael numbers less than $10^{24}$ and we provide some statistics on these numbers.

math.NT↗

arXiv2024

Advances in Tabulating Carmichael Numbers

We report that there are $49679870$ Carmichael numbers less than $10^{22}$ which is an order of magnitude improvement on Richard Pinch's prior work. We find Carmichael numbers of the form $n = Pqr$ using an algorithm bifurcated by the size of $P$ with respect to the tabulation bound $B$. For $P < 7 \cdot 10^7$, we found $35985331$ Carmichael numbers and $1202914$ of them were less than $10^{22}$. When $P > 7 \cdot 10^7$, we found $48476956$ Carmichael numbers less than $10^{22}$. We provide a comprehensive overview of both cases of the algorithm. For the large case, we show and implement asymptotically faster ways to tabulate compared to the prior tabulation. We also provide an asymptotic estimate of the cost of this algorithm. It is interesting that Carmichael numbers are worst case inputs to this algorithm. So, providing a more robust asymptotic analysis of the cost of the algorithm would likely require resolution of long-standing open questions regarding the asymptotic density of Carmichael numbers.

math.NT↗

arXiv2020

Average liar count for degree-2 Frobenius pseudoprimes

In this paper we obtain lower and upper bounds on the average number of liars for the Quadratic Frobenius Pseudoprime Test of Grantham, generalizing arguments of Erdős and Pomerance, and Monier. These bounds are provided for both Jacobi symbol plus and minus cases, providing evidence for the existence of several challenge pseudoprimes.

math.NT↗

arXiv2018

Fast tabulation of challenge pseudoprimes

We provide a new algorithm for tabulating composite numbers which are pseudoprimes to both a Fermat test and a Lucas test. Our algorithm is optimized for parameter choices that minimize the occurrence of pseudoprimes, and for pseudoprimes with a fixed number of prime factors. Using this, we have confirmed that there are no PSW challenge pseudoprimes with two or three prime factors up to $2^{80}$. In the case where one is tabulating challenge pseudoprimes with a fixed number of prime factors, we prove our algorithm gives an unconditional asymptotic improvement over previous methods.

math.NT↗

arXiv2013

Constructing Carmichael numbers through improved subset-product algorithms

We have constructed a Carmichael number with 10,333,229,505 prime factors, and have also constructed Carmichael numbers with k prime factors for every k between 3 and 19,565,220. These computations are the product of implementations of two new algorithms for the subset product problem that exploit the non-uniform distribution of primes p with the property that p-1 divides a highly composite Λ.

math.NT↗

arXiv2013

Counting composites with two strong liars

The strong probable primality test is an important practical tool for discovering prime numbers. Its effectiveness derives from the following fact: for any odd composite number $n$, if a base $a$ is chosen at random, the algorithm is unlikely to claim that $n$ is prime. If this does happen we call $a$ a liar. In 1986, Erdős and Pomerance computed the normal and average number of liars, over all $n \leq x$. We continue this theme and use a variety of techniques to count $n \leq x$ with exactly two strong liars, those being the $n$ for which the strong test is maximally effective. We evaluate this count asymptotically and give an improved algorithm to determine it exactly. We also provide asymptotic counts for the restricted case in which $n$ has two prime factors, and for the $n$ with exactly two Euler liars.

math.NT↗

arXiv2013

Lifting Automorphisms of Quotients by Central Subgroups

Given a finitely presented group $G$, we wish to explore the conditions under which automorphisms of quotients $G/N$ can be lifted to automorphisms of $G$. We discover that in the case where $N$ is a central subgroup of $G$, the question of lifting can be reduced to solving a certain matrix equation. We then use the techniques developed to show that $Inn(G)$ is not characteristic in $Aut(G)$, where $G$ is a metacyclic group of order $p^n$, $p\neq 2$.

math.GR↗

arXiv2012

Division algorithms for the fixed weight subset sum problem

Given positive integers $a_1,..., a_n, t$, the fixed weight subset sum problem is to find a subset of the $a_i$ that sum to $t$, where the subset has a prescribed number of elements. It is this problem that underlies the security of modern knapsack cryptosystems, and solving the problem results directly in a message attack. We present new exponential algorithms that do not rely on lattices, and hence will be applicable when lattice basis reduction algorithms fail. These algorithms rely on a generalization of the notion of splitting system given by Stinson. In particular, if the problem has length $n$ and weight $\ell$ then for constant $k$ a power of two less than $n$ we apply a $k$-set birthday algorithm to the splitting system of the problem. This randomized algorithm has time and space complexity that satisfies $T \cdot S^{\log{k}} = O({n \choose \ell})$ (where the constant depends uniformly on $k$). In addition to using space efficiently, the algorithm is highly parallelizable.

math.CO↗