OFFSET
1,1
COMMENTS
All terms of this sequence are terms of A173703 (2-Lehmer numbers) and all Lehmer numbers (if there are any) are contained in this sequence.
LINKS
Max Alekseyev, Table of n, a(n) for n = 1..114
EXAMPLE
phi(247105) = 194688 divides 2 * 13 * 247104.
MATHEMATICA
divQ[n_] := AnyTrue[Select[Divisors[n - 1], SquareFreeQ]*(n - 1), Divisible[#, EulerPhi[n]] &]; Select[Range[250000], CompositeQ[#] && divQ[#] &] (* Amiram Eldar, Oct 14 2020 *)
PROG
(PARI) is(n)={my(s=denominator((n-1)/eulerphi(n))); !isprime(n) && issquarefree(s) && ((n-1)%s==0) && n>1}
{ forcomposite(n=1, 2^28, if(is(n), print1(n, ", "))) }
CROSSREFS
KEYWORD
nonn
AUTHOR
Tomohiro Yamada, Sep 28 2020
EXTENSIONS
More terms from Amiram Eldar, Oct 14 2020
STATUS
approved