Most outstanding prime

I have 4 distinct prime numbers .
The sum of these 4 numbers is also a prime number.

The product of these 4 numbers is a/an ___________ \text{\_\_\_\_\_\_\_\_\_\_\_} number.

even odd

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3 solutions

Let the primes be p , q , r , s p,q,r,s .And let p + q + r + s = t p+q+r+s=t where t t is also a prime.

Suppose all the primes p , q , r , s p,q,r,s are odd.Then p + q + r + s = t p+q+r+s=t will be even according as parity as (Odd+Odd)+(Odd+Odd)=Even+Even=Even \text{(Odd+Odd)+(Odd+Odd)=Even+Even=Even}

But that implies that t t is an even prime number.Note that as p , q , r , s p,q,r,s are all greater than or equal to 3 (since they are odd),their sum must be greater than or equal to 12.This implies that t t is an even prime number greater than 12,contradiction.

Hence t t is odd and at least one of the prime p , q , r , s p,q,r,s is even.Hence their product p q r s pqrs will be even as well.

Yup! You applied and explained parity of integers very nicely!

A common misconception that people make is to assume that ALL prime numbers are odd, which is not true because 2 is an (and only) even prime number.

Pi Han Goh - 4 years, 3 months ago
Razzi Masroor
Feb 14, 2017

Since all primes are odd except for 2, if we had all of the primes be odd, since odd+odd=even and even+even=even, the sum of these 4 odd primes would be even so we can not have all of the primes be odd, this means that one of the numbers is 2.Since (even)(odd)=even, the product must be even.Note that the numbers 2, 3, 5, 7 and 2, 3, 11, 7 also work so there is more than one pair of numbers satisfying these limitations

Edwin Gray
Apr 7, 2019

If the sum of the four primes is also a prime, then they cannot all be odd, for there sum would be even; so one of the primes must be 2, and the product is even.

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