Euler problem 46

It was proposed by Christian Goldbach that every odd composite number can be written as the sum of a prime and twice a square.

9 = 7 + 21²
15 = 7 + 22²
21 = 3 + 23²
25 = 7 + 23²
27 = 19 + 22²
33 = 31 + 21²

It turns out that the conjecture was false.

What is the smallest odd composite that cannot be written as the sum of a prime and twice a square?

Performance improvement:

Add .Tolist() extension result in 2 times faster execution.

List<int> primes = new PrimeNumberSieve().ToList(); // 15 ms -> 8 ms.

Problem46 =        5777 elapsed time:   8 ms. Test Passed.