Primes of the form x2 + ny2.

p = .

p = 4k + 1,  p = 8k + 1 / 8k + 3,  p = 3k + 1,  p = 20k + 1 / 20k + 9,  p = 24k + 1 / 24k + 7,  p = 7k + 1 / 7k + 2 / 7k + 4,  p = 40k + 1 / 40k + 9 / 40k + 11 / 40k + 19.

rule is here.