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.

343 : 47

The logic followed here Is :

second number × 9 = Ist number

441 : 49 = 49 × 9 = 441

729 : 81 = 81 × 9 = 729

369 : 41 = 41 × 9 = 369

343 : 47 = 47 ×  9 = 423 ≠ 343