The OEIS Foundation is grateful to everyone who made a donation during our Annual Appeal. Visit the new and spectacular Pictures from the OEIS page!
1,1
Appears to be the numbers k such that the sequence 5^n mod k has period length k-1. All terms are congruent to 2 or 3 mod 5. - Gary Detlefs, May 21 2014
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Index entries for primes by primitive root
pr=5; Select[Prime[Range[200]], MultiplicativeOrder[pr, # ] == #-1 &]
Sequence in context: A045333 A040141 A235627 * A113425 A245590 A110480
Adjacent sequences: A019332 A019333 A019334 * A019336 A019337 A019338
nonn
David W. Wilson
approved