OFFSET
1,1
COMMENTS
McNew and Wright proved that this sequence is infinite.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Nathan McNew and Thomas Wright, Infinitude of k-Lehmer numbers which are not Carmichael, International Journal of Number Theory, Vol. 12, No. 7 (2016), pp. 1863-1869; preprint, arXiv:1508.05547 [math.NT], 2015.
EXAMPLE
15 = 3 * 5 is a term since it is composite and not a Carmichael number, and rad(phi(15)) = rad(8) = 2 divides 15 - 1 = 14.
MATHEMATICA
rad[n_] := Times @@ (First@# & /@ FactorInteger[n]); Select[Range[4000], Divisible[#-1, rad[EulerPhi[#]]] && !Divisible[#-1, CarmichaelLambda[#]] &]
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Mar 14 2020
STATUS
approved