Suppose that an infinite set
A occupies at most
residue
classes modulo
p, for every sufficiently large prime
p. The squares, or
more generally the integer values of any quadratic, are an example of such a
set. By the large sieve inequality the number of elements of
A that are at
most
X is
, and the quadratic examples show that this is sharp.
The simplest
... [Show full abstract] form of the inverse large sieve problem asks whether they are the
only examples. We prove a variety of results and formulate various conjectures
in connection with this problem, including several improvements of the large
sieve bound when the residue classes occupied by A have some additive
structure. Unfortunately we cannot solve the problem itself.