1,1

David A. Cox, "Primes of the Form x^2 + n y^2", Wiley, 1989, p. 60.

G. B. Mathews, Theory of Numbers, Chelsea, no date, p. 263.

Table of n, a(n) for n=1..4.

(PARI) ok(n)={my(u=quadclassunit(-4*n).cyc); #u==4 && !select(t->t<>2, u)} \\ Andrew Howroyd, Jun 09 2018

A subsequence of A000926.

Cf. A033266, A033267, A033268.

Sequence in context: A102793 A144770 A068546 * A272595 A179670 A092002

Adjacent sequences: A033266 A033267 A033268 * A033270 A033271 A033272

nonn,fini,full

N. J. A. Sloane

approved