Upper bounds on the solutions to $n=p+m^2$

Abstract

Hardy and Littlewood conjectured that every large integer $n$ that is not a square is the sum of a prime and a square. They believed that the number $\mathcal{R}(n)$ of such representations for $n=p+m^2$ is asymptotically given by \mathcal{R}(n) \sim \frac{\sqrt{n}}{\log n}\prod_{p=3}^{\infty}(1-\frac{1}{p-1}(\frac{n}{p})), where $p$ is a prime, $m$ is an integer, and $(\frac{n}{p})$ denotes the Legendre symbol. Unfortunately, as we will later point out, this conjecture is difficult to prove and not \emph{all} integers that are nonsquares can be represented as the sum of a prime and a square. Instead in this paper we prove two upper bounds for $\mathcal{R}(n)$ for $n\le N$. The first upper bound applies to \emph{all} $n\le N$. The second upper bound depends on the possible existence of the Siegel zero, and assumes its existence, and applies to all $N/2<n\le N$ but at most $\ll N^{1-{\delta }_1}$ of these integers, where $N$ is a sufficiently large positive integer and $0<{\delta }_1\le 0.000025$.