OFFSET
1,1
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
MATHEMATICA
pr = -18; Select[Range[2, 800], MultiplicativeOrder[pr, #] == EulerPhi[#] &]
PROG
(PARI) is(n)=if(gcd(n, 6)>1, return(0)); my(p=eulerphi(n)); znorder(Mod(-18, n), p)==p \\ Charles R Greathouse IV, Nov 26 2014
CROSSREFS
Cf. numbers with positive primitive root r: A167791 (r=2), A167792 (r=3), A167793 (r=5), A167794 (r=6), A167795 (r=7), A167796 (r=8), A167797 (r=10), A240028 (r=11), A240030 (r=12), A240032 (r=13), A240094 (r=14), A240096 (r=15), A240101 (r=17), A240103 (r=18).
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Apr 01 2014
STATUS
approved