How can I make the following RegEx pattern?

I need a regex pattern.

XXX[NUMBER]

For Example:
XXX[123456]

or

[NUMBER]XXX

For Example:
[123456]XXX

What is the pattern to match these two pattern ?

I tried the following way, but I can only add the parentheses to the beginning of the numbers:

[\[0-9]{0,35}[X]{0,35}|[X]{0,35}[\[0-9]{0,35}

Kind regards.

>Solution :

If you want just the numbers with the parenthesis:

var regex = new Regex(@"\[\d+\]");