cp's OEIS Frontend

Please look into A234001 for a more detailed description.

If n is squarefree and n == 1 (mod 4) or n == 2 (mod 4), then a(n) = 1.

If p^2 divides n for some prime p, a(n) is a multiple of p.

If n == 3 (mod 8), then a(n) is a multiple of 4 because numbers of the form x^2+n*y^2 cannot have any prime factors that are congruent to 2+n (mod 2n) raised to an odd power.

If n == 7 (mod 8), then a(n) is a multiple of 2 because numbers of the form x^2+n*y^2 can have prime factors that are congruent to 2+n (mod 2n) raised to an odd power, but they cannot be congruent to 2 (mod 4). So, we need to characterize the prime factor of 2 from the remaining prime factors that are congruent to 2+n (mod 2n) separately.