The second Hardy-Littlewood conjecture asserts that for integers ,
where
is the prime counting function (Hardy and
Littlewood 1923). In other words, an interval
of length
contains at most as many primes
as the initial interval
.
Hensley and Richards (1974) constructed sets of more than integers in a half-open interval
whose residues omit at least
one class modulo each prime number. The k-tuple
conjecture, the first of the Hardy-Littlewood
conjectures, predicts that infinitely many translates of such a set
consist entirely of primes. Any such translate sufficiently
far to the right would violate the second Hardy-Littlewood conjecture.