Fix number_of_divisors() to return correct results when n > 1

[gr8rithic]

Describe your change:

Fixes #5999

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints.
• All functions have doctests that pass the automated testing.
• All new algorithms have a URL in its comments that points to Wikipedia or other similar explanation.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #5999 }.

[cclauss]

Please add tests that would fail on the current code but pass on the proposed code so we have proof this change is required.

The current title of this PR shows little respect to the reader because it forces them to manually look up what #5999 refers to. I will make changes to demonstrate a better practice that gives the reviewer single-click access to #5999 and also enables autoclosing of the issue when the PR is merged as discussed at:
https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[cclauss]

In preparation for that denial-of-service attack that is Hacktoberfest, I am closing all pull requests that have failing tests.