A147578 - OEIS

%I #14 Dec 22 2020 02:14:28

%S 15015,45045,75075,105105,135135,165165,195195,225225,315315,375375,

%T 405405,495495,525525,585585,675675,735735,825825,945945,975975,

%U 1126125,1156155,1216215,1366365,1486485,1576575,1756755,1816815,1876875,2027025,2147145,2207205,2477475

%N Numbers with exactly 5 distinct odd prime divisors {3,5,7,11,13}.

%C Numbers k such that phi(k)/k = m

%C ( Family of sequences for successive n odd primes )

%C m=2/3 numbers with exactly 1 distinct prime divisor {3} see A000244;

%C m=8/15 numbers with exactly 2 distinct prime divisors {3,5} see A033849;

%C m=16/35 numbers with exactly 3 distinct prime divisors {3,5,7} see A147576;

%C m=32/77 numbers with exactly 4 distinct prime divisors {3,5,7,11} see A147577;

%C m=384/1001 numbers with exactly 5 distinct prime divisors {3,5,7,11,13} see A147578;

%C m=6144/17017 numbers with exactly 6 distinct prime divisors {3,5,7,11,13,17} see A147579;

%C m=3072/323323 numbers with exactly 7 distinct prime divisors {3,5,7,11,13,17,19} see A147580;

%C m=110592/323323 numbers with exactly 8 distinct prime divisors {3,5,7,11,13,17,19,23} see A147581.

%H Amiram Eldar, <a href="/A147578/b147578.txt">Table of n, a(n) for n = 1..10000</a>

%F Sum_{n>=1} 1/a(n) = 1/5760. - _Amiram Eldar_, Dec 22 2020

%t a = {}; Do[If[EulerPhi[x]/x == 384/1001, AppendTo[a, x]], {x, 1, 1000000}]; a

%Y Cf. A000010 (EulerPhi), A060735, A143207, A147571-A147575, A147576-A147580.

%K nonn

%O 1,1

%A _Artur Jasinski_, Nov 07 2008

%E More terms from _Amiram Eldar_, Mar 11 2020