OFFSET
1,2
COMMENTS
Subsequence of A003277 (cyclic numbers).
Let L(x) = exp(log x log log log x/log log x). McNew shows that there are at most x/L(x)^(1+o(1)) members of this sequence up to x. - Charles R Greathouse IV, Oct 08 2012
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
José María Grau and Antonio M. Oller-Marcén, On k-Lehmer numbers, Integers, 12(2012), #A37
Nathan McNew, Radically weakening the Lehmer and Carmichael conditions (2012)
EXAMPLE
15 is in the sequence because phi(15)=8, rad(8)=2 and 2 divides 15-1.
MATHEMATICA
rad[n_]:=Times@@Transpose[FactorInteger[n]][[1]]; Select[Range[1000], Mod[#-1, rad[EulerPhi[#]]]==0&]
PROG
(PARI) rad(n)=n=factor(n); prod(i=1, #n[, 1], n[i, 1]);
for(n=1, 1e4, if((n-1)%rad(eulerphi(n))==0, print1(n", "))) \\ Charles R Greathouse IV, Jul 04 2011
(PARI) is(n)=my(p=eulerphi(n), g=n); n--; while((g=gcd(p, g))>1, p/=g); p==1 && n \\ Charles R Greathouse IV, Mar 03 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
José María Grau Ribas, Mar 13 2011
STATUS
approved