1. Write a Python program to check whether a string represent an integer or not.

Example:

Please enter a string: Python # this is user input

This is not an integer.

2. Write a Python function to remove the character of index n from a non empty string. 

3. Write a Python program which prompts the user to create a user account and checks whether the provided user name and password are legal.

Note: a user name should start with a letter and only consists of letters and numbers. The length should be between 6 and 12; a password should start with a letter and only consists of letters, numbers of the underscore symbol "_". The length should be between 8 to 16.

4. Write a Python function to get the first half of a specified string of even length.  Suppose the input string is "Python", after calling the function, we should see the output "Pyt".