Vlookup or If/Then to return a substitute cell for a cell that matches itself in a range

I know the title might seem confusing. This is what I'm trying to do.

I have a list of numbers in column A. Everything to the right of column A in the same row can be represented by the A cell. So A2:A40 are to be represented by A1, etc. I have another sheet where I have the list of all possible numbers. I want to run a formula that will return the value in the A1 cell for all numbers that have matches in A row. So in my other sheet, if A2 comes up, in the column next to it, I want A1 to appear. I'll attach a book to show what I mean. There are two tabs.

Thanks.