I'm sure there is a way to do this with VLOOKUP or a similar function, I just
don't know how.....

I want to compare two lists of numbers. If the second list does not contain
the number, I want to return the value "no" in the cell to the right of the
first number.

Here's an example:

A B C D

List 1 List 2

1 1234 no 1235
2 1235 1237
3 1236 no 1238
4 1237
5 1238
6 1239 no