Choose the one which does not belong to the group

The pattern which is being followed in the above question is:

n: (n x 4) - 1

5:18 → 5 x 4 - 1 ≠ 18

6:23 → 6 x 4 - 1 = 23

3:11 → 3 x 4 - 1 = 11

1:3 → 1 x 4 - 1 = 3

Thus, the answer stands to be 5:18 as it does not follow the pattern.