They are:
8, 12, 18, 20, 27,
28, 30, 42, 44, 45,
50, 52, 63, 66, 68,
70, 75, 76, 78, 92,
98, 99.
There are some that have more than 3 - which means that they do have 3.
[That last part is like the old riddle: how many months have 28 days - and the answer is all of them. Eleven have more than 28, but they do have 28.]
There are 4 prime numbers under ten.
30, 42, 66, 70 and 78.
There are 15 prime numbers less than 50.
By definition, a product of two primes has atwo factors (other than 1 and itself) and so it cannot be prime. So the set is not closed.
No.
There are no prime numbers anywhere that are divisible by 2 and 7.
There are 4 prime numbers under ten.
Numbers that have exactly 2 factors under 10 are prime numbers. Prime numbers are integers greater than 1 that have no positive divisors other than 1 and themselves. Examples of prime numbers under 10 are 2, 3, 5, and 7. These numbers have only two factors, 1 and the number itself.
Prime Numbers under 6 are 2,3,5
30, 42, 66, 70 and 78.
There are 34 prime numbers under 140.
The prime numbers under 16 are 2,3,5,7,11 & 13.
Odd prime numbers under 15 are prime numbers that are greater than 2 and do not have any factors other than 1 and themselves. The odd prime numbers under 15 are 3, 5, 7, 11, and 13. These numbers cannot be divided evenly by any other number except 1 and themselves, making them prime.
Numbers under 100 that have 12 factors must be in the form of ( p_1^{11} ) or ( p_1^3 \times p_2^2 ), where ( p_1 ) and ( p_2 ) are distinct prime numbers. The prime factorization of 12 is ( 2^2 \times 3 ). Thus, the numbers under 100 with exactly 12 factors are ( 2^{11} = 2048 ) and ( 2^3 \times 3 = 24 ).
If you look at the related question, "What are the prime factors of the numbers from 1 to 200?" (provided in the link below), take the prime numbers, and show them with multiplication signs between them, then you will have the prime factorization. Examples: The prime factors of 15 are 3 and 5. Therefore, the prime factorization is 3 x 5. The prime factors of 42 are 2, 3, and 7. Therefore, the prime factorization is 2 x 3 x 7. The prime factors of 64 are 2, 2, 2, 2, 2, and 2. Therefore, the prime factorization is 2 x 2 x 2 x 2 x 2 x 2. If you want the prime factorization of a specific number, it is sometimes listed under questions of the form, "What are the prime factors of __?" or "What are the factors of __?" or "What are the factors and prime factors of __?"
The prime squares, like 4, 9, 25 and 49
Any product of 2 prime numbers will have 4 factors. Any prime number to the 3rd power will have 4 factors.6, 8, 10, 14, 15, 21, 22, 26, 27, 33, 34, 35, 38, 39, 46, 51, 55, 57, 58, 62, 65, 69, 74, 77, 82, 85, 86, 87, 91, 93, 94, 95