Which of the following is not a prime number
157
1057
263 or
3163

Prime numbers are numbers that are simplified, or rather, cannot be divided into any smaller numbers and has only 1 and itself (excluding 1, as it is NOT prime).

For example, 2 is a prime number, as it has 1 and itself for the only factors.
4 is NOT a prime number, as it has more than 2 factors; 1&4, 2&2.

Although, we are looking for a number that is NOT prime (composite).

157 is prime, as 3, 5, 7, 9, 11, and 13 cannot go into it (main odd multiples).

1057 is NOT prime, as it can divide into 7 by 151.

1057 is your answer.

I hope this helps!