What is the sum of the unique prime factors of 9991?
Wait whoops I meant 200
So, any non-prime number is formed by a product of prime numbers, then if 9991 isn´t prime, we can find its factors. Given that 9991 is a four-digit number, we can start dividing it by primes that are at least bigger than 90 (given that 90^2= 8100), so the first prime above 90 is 97. So 9991/97=103 and 103 is a prime and the 2nd prime factor. Therefore, the sum of the primes is 103 + 97 = 200.
list of prime numbers between 1 and 100: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, and 97.
200 I am in mathcounts and had it for homework
Yeah it is 200
Wow, a lot of Mathcounts people here
Hi can some pls show the method of solving it.
"What is the sum of the unique prime factors of 9991?"