Lemma.
Assuming that:
f
:
ℕ
→
ℂ
satisfying
|
f
(
n
)
|
≤
n
o
(
1
)
Then
D
f
(
s
)
converges absolutely for
Re
(
s
)
>
1
and defines an analytic function for
Re
(
s
)
>
1
.