A245042 Primes of the form (k^2+4)/5.

17, 73, 89, 193, 337, 521, 953, 1009, 1249, 1657, 2377, 2833, 3329, 3433, 4441, 4561, 5849, 6553, 7297, 8081, 8737, 9769, 11617, 12401, 12601, 13417, 15569, 16937, 17881, 18121, 20353, 21649, 27529, 28729, 29033, 30577, 33457, 35449, 36809, 46273, 49801

Offset: 1

Author

Chai Wah Wu, Jul 10 2014

Keywords

• nonn

Comments

Also equal to primes p such that 5*p-4 is a perfect square.

Links

• Chai Wah Wu, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A154418.

Cf. A154616, A002327, A066436.

Programs

Mathematica

Select[(Range[500]^2+4)/5,PrimeQ] (* Harvey P. Dale, Jul 13 2014 *)

Python

import sympy
L = (k**2 + 4 for k in range(10**3))
[n//5 for n in L if n % 5 == 0 and sympy.ntheory.isprime(n//5)]