cp's OEIS Frontend

A249396 Composite numbers whose Euler totient divides the sum of the Euler totients of the numbers less than n that are relatively prime to n.

%I A249396 #25 Nov 11 2014 21:04:18
%S A249396 9,75,135,265,1383,6585,17251,165615,503111,856195
%N A249396 Composite numbers whose Euler totient divides the sum of the Euler totients of the numbers less than n that are relatively prime to n.
%C A249396 No more terms < 10^6.
%e A249396 Numbers coprime to 9 are 1, 2, 4, 5, 7, 8 and phi(9) = 6. Then, phi(1) + phi(2) + phi(4) + phi(5) + phi(7) + phi(8) = 1 + 1 + 2 + 4 + 6 + 4 = 18 and 18/6 = 3.
%p A249396 with(numtheory): P:=proc(q) local a,k,n; for n from 2 to q do
%p A249396 if not isprime(n) then a:=0;
%p A249396 for k from 1 to n do if gcd(k,n)=1 then a:=a+phi(k); fi; od;
%p A249396 if type(a/phi(n),integer) then print(n); fi; fi; od; end: P(10^9);
%o A249396 (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
%Y A249396 Cf. A000010, A053570, A249397.
%K A249396 nonn,more
%O A249396 1,1
%A A249396 _Paolo P. Lava_, Oct 27 2014
%E A249396 a(8) from _Ray Chandler_, Nov 07 2014
%E A249396 a(9)-a(10) from _Ray Chandler_, Nov 11 2014