Identify the missing term in the following number series:
13, 4, 26, 8, 52, 7, 104, ?

The series is constructed in pairs where the second number is the sum of the digits of the preceding number.
Let us evaluate the pairs:

* $\text{Pair 1}:13\to 1+3=4$
* $\text{Pair 2}:26\to 2+6=8$
* $\text{Pair 3}:52\to 5+2=7$
* $\text{Pair 4}:104\to 1+0+4=5$

Hence, the missing term following $104$ is $5$.