Theorem 1.5
(Dirichlet’s divisor problem)
.
For
x
≥
2
,
∑
n
≤
x
τ
(
n
)
=
x
log
x
+
(
2
γ
−
1
)
x
+
O
(
x
1
∕
2
)
where
γ
is
Euler’s constant
.