A105877 Primes for which -5 is a primitive root.

2, 11, 17, 19, 37, 53, 59, 73, 79, 97, 113, 131, 137, 139, 151, 157, 173, 179, 193, 197, 233, 239, 257, 277, 293, 311, 317, 331, 353, 359, 373, 397, 419, 431, 433, 439, 479, 491, 499, 557, 571, 577, 593, 599, 613, 617, 619, 653, 659, 673, 677, 719, 751, 757, 773, 797, 811

Offset

1,1

Comments

Conjecture: the penultimate digit of a(n) is always odd. This characteristic seems to be proper of primes for which -5*n^2 is a primitive root. - Davide Rotondo, Oct 26 2024

For any n > 1, a(n) == 11, 13, 17, or 19 (mod 20), which implies the conjecture above. - Max Alekseyev, Nov 01 2024

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Index entries for primes by primitive root

Mathematica

pr=-5; Select[Prime[Range[200]], MultiplicativeOrder[pr, # ] == #-1 &]

Crossrefs

Sequence in context: A103336 A019402 A038927 * A309499 A173638 A018420

Adjacent sequences: A105874 A105875 A105876 * A105878 A105879 A105880

Keyword

nonn

Author

N. J. A. Sloane, Apr 24 2005

Status

approved