OFFSET
1,1
COMMENTS
No more terms < 10^6.
EXAMPLE
Numbers not coprime to 161 are 7, 14, 21, 23, 28, 35, 42, 46, 49, 56, 63, 69, 70, 77, 84, 91, 92, 98, 105, 112, 115, 119, 126, 133, 138, 140, 147, 154, 161 and the sum of their Euler totients is 1320; phi(161) = 132 and 1320/132 = 10.
MAPLE
with(numtheory): P:=proc(q) local a, k, n; for n from 1 to q do
if not isprime(n) then a:=0;
for k from 1 to n do if gcd(k, n)>1 then a:=a+phi(k); fi; od;
if type(a/phi(n), integer) then print(n); fi; fi; od; end: P(10^9);
PROG
(PARI) isok(n) = (n!=1) && !isprime(n) && (sum(k=1, n-1, if (gcd(k, n) != 1, eulerphi(k), 0)) % eulerphi(n) == 0); \\ Michel Marcus, Oct 29 2014
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Paolo P. Lava, Oct 27 2014
EXTENSIONS
a(11)-a(12) from Michel Marcus, Nov 01 2014
a(13)-a(19) from Michel Marcus, Nov 03 2014
a(20) from Ray Chandler, Nov 04 2014
STATUS
approved