In Sheet2 you can use column A t list the number values (7, 8, 12 etc) and column B to list the appropriate text values that they get converted into (d12, 2d6, 2d10 etc). Then in A2 of Sheet1 you can use this formula:

=VLOOKUP(A1,Sheet2!$A:$B,2,0)

Hope this helps.

Pete