s
u
m
m
a
t
i
o
n
f
u
n
c
t
i
o
n
-
k
e
3
k
2
s
i
n
(
k
)
1
l
o
g
(
k
+
1
)
t
e
r
m
s
i
n
s
e
r
i
e
s
2