Consider the series: 2, 3, 5, 7, 11, 13, 17, 19, 21, 23, 29 Find the number which is different from other similar numbers.

29 23 19 21

21

All these numbers are prime numbers 2, 3, 5, 7, 11, 13, 17, 19, 23, 29 only 21 is odd as it is not a prime number. Prime number is a whole number greater than 1 that cannot be exactly divided by any whole number other than itself and 1