# Algorithm to find prime number of a specific even number in Goldbach's conjecture [closed]

According to Goldbach's conjecture:

Every even integer greater than 2 can be expressed as the sum of two primes.

What is the most efficient algorithm which takes an even number and gives the two prime?

## closed as off-topic by Matthew Conroy, Claude Leibovici, JonMark Perry, TheSimpliFire, Parcly TaxelFeb 14 '18 at 14:02

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• Certainly, such algorithm exists, a naive one is to list all prime number lesser than that even number and check summation which of those are our even number. – monalisa Feb 13 '18 at 17:14
• This algorithm is the same of mine, It is trivial and inefficient, I need a more efficient algorithm for a decimal number in order of 300 digits. – monalisa Feb 13 '18 at 18:18
• I guess sieve of eratosthenes will be quite efficient. When trying to find a decomposition of N, sieve the interval [1,m] and [N-m,N] for sufficiently large m. Then check pairs that remain. Should be quite fast, even for numbers as big as 300 digits – Michael Stocker Feb 13 '18 at 18:54
• are you kidding, do you know what happens if the resultant prime numbers would be twin primes in the middle of the interval? In that case, I have tested all numbers! – monalisa Feb 13 '18 at 19:10
• Conjecturally, there will always be a pair with one prime small. Quoting Wikipedia, "3,325,581,707,333,960,528 is the smallest number that has no Goldbach partition with a prime below 9781". Hence we would expect the brute-force search to be somewhat effective. – Wojowu Feb 13 '18 at 20:01