если число четное то его можно представить как сумму двух  простых чисел, а если оно нечетно то либо как сумму 2 простых либо как 3 + (a + b), a, b - простые, как определить для нечетного числа надо 3 или 2 числа
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if the number is even then it can be written as the sum of two primes, and if it is odd then either as the sum of two simple or as 3 + (a + b), a, b - prime.
 How to determine the odd numbers must be 3 or 2 numbers?

The sum of 2 odd numbers is always an odd number.

To have 2 numbers sum up to an odd number, one needs an even number and an odd number. In this case, 2 + (n-2) (because 2 is the only even prime).

Now, I'm stuck on how to solve the problem fast for even numbers