Three of the following four are alike in a certain way and thus form a group. Which is the one that does NOT belong to that group?
(NOTE : Operations should be performed on the whole numbers, without breaking down the numbers into its constituent digits. E.g., 13 - Operations on 13 such as adding / subtracting / multiplying etc. to 13 can be performed. Breaking down 13 into 1 and 3 and then performing mathematical operations on 1 and 3 is not allowed)
1
2 - 6
2
4 - 20
3
5 - 30
4
8 - 75