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In 1741 Christian Goldbach conjectured that every even number could be written as a sum of two primes. [At the time 1 was considered a prime and so 2 = 1 + 1.] The conjecture has not been proven so there may be even numbers which cannot be so written. Also every number which is greater than 5 and is one fewer than a multiple of 6 cannot be so written.

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โˆ™ 8y ago
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โˆ™ 10y ago

There could be many answers for this question. One of them is 30 which is a sum of 15 and 15, both non-prime.

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Q: What composite numbers are not the sum of two prime numbers?
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Related questions

If you add a prime number to itself is the the sum composite or prime?

The sum of two prime numbers will be composite unless one of the prime numbers is 2.


Is the sum of any two prime numbers always a composite number?

The sum of any two prime numbers is not always a composite number. The sum of 2 and 11 is 13, and 13 is a prime number, not a composite number.


What is the term for the sum of two prime numbers?

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When adding 2 prime number will the answer be prime?

The sum of any two prime numbers may or may not be prime. The sum of the two prime numbers 2 and 3 is the prime number 5, and the sum of the two prime numbers 5 and 7 is the composite number 12.


Are composite numbers closed under addition?

No, they are not. You can add two composite numbers, 15 and 14 for example, and get a sum, 29, that is prime.


Is the sum of two prime numbers can be composite?

Well, honey, let me break it down for you. The sum of two prime numbers can definitely be composite. Take 2 and 3 for example - both prime, but when you add them together, you get 5, which is still prime. But toss in 2 and 4, both prime, and you get 6, which is as composite as it gets. So, yes, the sum of two prime numbers can absolutely be composite.


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