What will be the next number? 3, 5, 7, 11, 13, 17…….

A prime number is a natural number greater than 1 whose only two factors are 1 and itself. When a series lists consecutive prime numbers in increasing order, the next term is found by testing successive natural numbers against this two-factor rule until one qualifies.

The given series 3, 5, 7, 11, 13, 17 lists consecutive prime numbers, so the next term must be the very next prime number greater than 17.

1. 18 = 2 × 9, so 18 has factors besides 1 and itself and is not prime.

2. 19 is not divisible by 2, 3, or any other number up to its square root (which is less than 5), so its only two factors are 1 and itself — 19 is prime.

3. Therefore the next term of the series is 19.

Checking the remaining options confirms this: 21 = 3 × 7 is composite, 20 = 2 × 10 is composite, and 23 is indeed prime but is the prime number that comes after 19, not the one immediately following 17.

Answer: 19.