Customer Name which can contain a string and integer

Hi all,

I am new to this forum and I decided to register as a I need help on below issue.

I am having a big set of customer names, and the customer names can have characters and integers.
The list is containing internal and external customer names and I can identify the internal ones if there are 4 numbers in a row. Unfortunately the numbers can be in different sections of the customer name it self.

Therefore I am wondering if there is any way to create a formula/function to return Y and N for internal customer names. Please see examples attached.

Thanks in advance
Flooo

Attached Images