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.

17 : 238

THE LOGIC;

1) 16 : 224,

(16x16) = 256 - (16x2) = 224

2) 21 : 399,

(21x21) = 441 - (21x2) = 399

3) 35 : 1155,

(35x35) = 1225 - (35x2) = 1155

4) 17 : 238,

(17x17) = 289 - (17x2) = 255 not 238

Thus, 17 : 238 is the odd one.