OFFSET
1,2
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
phi(21)=12, gcd(12,20)=4, 21 is divisible by {1,3,7,21}.
MAPLE
filter:= t -> igcd(numtheory:-phi(t), t-1) = numtheory:-tau(t):
select(filter, [$1..1000]); # Robert Israel, Mar 15 2019
PROG
(PARI) isok(n) = gcd(eulerphi(n), n-1) == numdiv(n); \\ Michel Marcus, May 30 2014
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
EXTENSIONS
Term 1 prepended by Michel Marcus, May 30 2014
STATUS
approved