Let
be the least upper bound of the numbers
such that
is bounded as
, where
is the Riemann zeta
function. Then the Lindelöf hypothesis states that
is the simplest function that is zero for
and
for
.
The Lindelöf hypothesis is equivalent to the hypothesis that (Edwards 2001, p. 186).
Backlund (1918-1919) proved that the Lindelöf hypothesis is equivalent to the statement that for every , the number of roots in the rectangle
grows less rapidly
than
as
(Edwards 2001, p. 188).