OFFSET
1,1
COMMENTS
A proper subset of the Carmichael numbers A002997.
If n is in the sequence, then n-1 is not squarefree.
Problem: are there infinitely many such numbers?
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
Select[Range[3, 10^6], Divisible[#-1, CarmichaelLambda[#] * GCD @@ (Divisors[#] - 1)] &] (* Amiram Eldar, Jun 26 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Thomas Ordowski and Altug Alkan, Apr 01 2017
STATUS
approved