23: The Root and the Ratio tests do not seem to be a good idea, as we do not readily see any approach to investigating the k-th root of the terms or their appropriate ratio. There is also no obvious candidate for comparison. On the other hand, the expression seems quite suitable for the Integral test.

If you do not like this, try to get some feeling for the situation by asking the following question: How do the terms look like for large values of k?

Next hint
Answer