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5 votes
1 answer
309 views

How often is the value of a quadratic polynomial equal to a sum of two integer squares?

Let $b:\mathbb N\to \{0,1\}$ be the indicator function of integers that are a sum of two non-zero integer squares. Let $f(t)\in \mathbb Z[t]$ be an irreducible polynomial of degree $2$ with positive l …
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4 votes
Accepted

Sieve bound for the sum of two squares

One can do a bit better. For simpler presentation assume that we instead consider the function $b'$ that is the indicator function of integers all of whose prime divisors are $1 \mod 4$. We have $b'\l …
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  • 3,062
4 votes

Divisor sums over values of binary forms of primes

An answer regarding the use of large sieve suggested by Lucia (too long for a comment). I guess her/his thought was along the following lines: The divisors $d$ of $p^2+q^2$ are of order $x^2$ and …
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  • 3,062
7 votes
2 answers
424 views

Divisor sums over values of binary forms of primes

Let $\tau$ be the divisor function, that is $$ \tau(n)=\sharp\{d \in \mathbb{N}, d|n\}. $$ I was wondering if anyone has ever proved an asymptotic estimate for the sum $$S(x):=\sum_{p,q\leq x}\tau(p …
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14 votes
4 answers
3k views

Jacobi's theorem on sums of two squares (reference request)

One of Jacobi's theorems states that the number of representations of a positive integer $n$ as a sum of two squares of integers equals $$4(d_1(n)-d_3(n)),$$ where the function $d_i$ counts the number …
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