The second number in the given number-pairs is obtained by performing certain mathematical operation(s) on the first number. The same operation(s) is/are followed in all the number-pairs, except one. Find that odd number-pair.

18 : 1620

The Logic;

1) 16 : 1024;

16 x2 = 32 x32 = 1024

2) 14 : 784;

14 x2 = 28 x28 =784

3) 18 : 1620;

18 x2 = 36 x36 = is not 1620

4) 12 : 576;

12 x2 = 24 x24 = 576

Thus, 18 : 1620 is correct.