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

81 : 730

The logic followed here is :

25 : 125

5² : 5³

49 : 343

7² : 7³

81 : 730

9² : 9³ (729 but 730 is given Odd)

36 : 216

6² : 6³