A090563 Numbers k such that 5*k^2 + 5*k + 1 is prime.

1, 2, 3, 4, 5, 6, 7, 11, 13, 14, 15, 16, 17, 19, 21, 22, 24, 25, 26, 30, 32, 35, 36, 38, 43, 44, 49, 52, 54, 55, 60, 61, 62, 63, 66, 69, 70, 71, 73, 74, 79, 80, 81, 82, 85, 87, 88, 93, 94, 101, 104, 106, 107, 109, 110, 112, 114, 115, 117, 123, 127, 128, 131, 135

Offset: 1

Author

Amarnath Murthy, Dec 11 2003

Keywords

• nonn

Links

• Robert Price, Table of n, a(n) for n = 1..2468

Crossrefs

Cf. A090562.

Programs

Mathematica

Do[s=5*n^2+5*n+1; If[PrimeQ[s], Print[n]], {n, 1, 1000}]
Select[Range[1000], PrimeQ[5 #^2 + 5 # + 1] &] (* Robert Price, Apr 13 2025 *)

PARI

isok(n) = isprime(5*n^2+5*n+1); \\ Michel Marcus, Apr 30 2016

Extensions

More terms from Labos Elemer, Dec 12 2003

Offset corrected by Arkadiusz Wesolowski, Aug 09 2011