Pick the odd one out from the given number series? 21, 24, 33, 49, 74

The given number series follows a pattern that,

$19 + 12 = 20 (\mathrm{not} 21)20 + 22 = 2424 + 32 = 3333 + 42 = 4949 + 52 = 74$

Hence, the odd number in the given number series is 21.