This paper by NC Ankeny mentions that " S. Chowla has proved that there exist infinitely many primes $k$ where the first $c_1\log k$ residues $(\bmod k)$ are all quadratic residues".

I recently found a proof of this here.

The proof constructs such primes using this idea:

- Consider numbers which satisfies these condition : $n=1\bmod 8$ and $n=1\bmod r_i$ where $r_i$ are first consecutive odd primes less than $y$.
- Let $R:= 8\prod r_i $ , clearly $n=1\bmod R$ by Chinese remainder theorem.
- By Linniks there exist a prime $p$ in this arithmetic progression $\{ 1+rk_j\}$ such that $p= \mathcal{O}(R^6)$.
- Note that for this prime all numbers less than $y$ are quadratic residue, since p $\equiv 1 \bmod 8 \implies \big(\frac{a}{p} \big) = \big( \frac{p}{a} \big) $.
- By prime number theorem it is easy to see that y = $O(\log p)$

But this analysis clearly doest rule out the possibility of having least quadratic non-residue $O(\log p)$ . Infact if we write all the constants and work it out than it doesn't even rule out the possibility of least quadratic non residue less than $10\log p$.

I want to know is this just what Chowla proved or there is a better argument for this. Any refrence for the same would be of great help.

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