$\"\"$

Theorem 9.9 :

$\"\"$ Term test for divergence: $\"\"$ then $\"\"$ diverges.

$\"\"$

The series is $\"\"$ .

If $\"\"$ convergence, then $\"\"$ .

The series is neither geomentric nor telescoping, so apply $\"\"$ Term test.

$\"\"$ .

Therefore, the sequence is divergent.

$\"\"$

$\"\"$ is divergent.