Ok probably a easy answer here, but I'm a excel Novice.

what I have is a series of numbers and what I want to find is what
Number are missing in between all the different numbers to complete a
whole set of number.

Example

I have: 1 2 6 7 9 13

How could I find whats missing as to make it straight count up from 1 to 13

And return from this example 3 4 5 8 10 11 12

Thanks for any help