A089747 Numbers n such that n^2 - 2n + 5 is prime.

0, 2, 4, 6, 8, 14, 16, 18, 28, 34, 36, 38, 46, 48, 58, 66, 68, 74, 86, 88, 96, 98, 104, 116, 118, 126, 136, 138, 148, 156, 164, 168, 178, 184, 194, 204, 208, 216, 218, 234, 236, 244, 246, 254, 256, 266, 268, 276, 278, 288, 294, 304, 308, 314, 318, 348, 358, 374

Offset: 1

Author

Giovanni Teofilatto, Jan 08 2004

Keywords

• nonn
• easy

References

• M. Cerasoli, F. Eugeni and M. Protasi, Elementi di Matematica Discreta, Bologna, 1988.
• Emanuele Munarini and Norma Zagaglia Salvi, Matematica Discreta, UTET, CittaStudiEdizioni, Milano, 1997.

Crossrefs

Cf. A005473 gives primes, A007591.

Programs

Magma

[n: n in [0..100]|IsPrime(n^2-2*n+5)] // Vincenzo Librandi, Nov 16 2010

Mathematica

Select[Range[0,400,2],PrimeQ[#^2-2#+5]&] (* Harvey P. Dale, Jan 04 2015 *)

PARI

is(n)=isprime(n^2-2*n+5) \\ Charles R Greathouse IV, Jun 13 2017

Formula

a(n) = A007591(n-1) + 1 for n > 1. [corrected by Georg Fischer, Jun 20 2020]