The number 49 is divisible by seven, so it is not a prime number. A prime number is a number that is only divisible by the number 1 and itself.
Prime numbers up to 100 are easily identifiable if you have memorized the multiplication tables through 12. Any even number, with the exception of the number two, is not a prime number because all even numbers are divisible by two. The next multiplier to be aware of would be three. The number three is prime, but using three as a factor removes the odd numbers nine, 15, 21, 27 and 33 as prime numbers. The number five is prime, but including it as a factor removes all odd numbers that end with a five, and so on.