A216286 - OEIS

A216286

Primes which cannot be written as x^2+5*y^2, where x > 0, y > 0.

2, 3, 5, 7, 11, 13, 17, 19, 23, 31, 37, 43, 47, 53, 59, 67, 71, 73, 79, 83, 97, 103, 107, 113, 127, 131, 137, 139, 151, 157, 163, 167, 173, 179, 191, 193, 197, 199, 211, 223, 227, 233, 239, 251, 257, 263, 271, 277, 283, 293, 307, 311, 313, 317, 331, 337, 347, 353, 359, 367, 373, 379, 383, 397, 419

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OFFSET

1,1

COMMENTS

This consists of 5 together with those primes which are not congruent to 1 or 9 (mod 20) (which are listed in A216277). - N. J. A. Sloane, Sep 04 2012

REFERENCES

David A. Cox, Primes of the Form x^2 + n y^2, Wiley, 1989. See Eq. (1.20), p. 19 and Eq. (2.22), p. 32. - N. J. A. Sloane, Sep 03 2012

LINKS

Table of n, a(n) for n=1..65.

CROSSREFS

Cf. A033205, A216277.

Sequence in context: A042966 A128898 A006514 * A086983 A303436 A334797

Adjacent sequences: A216283 A216284 A216285 * A216287 A216288 A216289

KEYWORD

nonn

AUTHOR

V. Raman, Sep 03 2012

STATUS

approved