What is a good reference for the story of congruences such as
$$\displaystyle \tau(n) \equiv \sigma(11)(n) \mod\ 691$$
with a conceptual explanation with connections to étale cohomology, etc?
What is a good reference for the story of congruences such as
$$\displaystyle \tau(n) \equiv \sigma(11)(n) \mod\ 691$$
with a conceptual explanation with connections to étale cohomology, etc?