A147575 - OEIS

%I #13 Nov 12 2020 10:35:10

%S 9699690,19399380,29099070,38798760,48498450,58198140,67897830,

%T 77597520,87297210,96996900,106696590,116396280,126095970,135795660,

%U 145495350,155195040,164894730,174594420,184294110,193993800,203693490,213393180,232792560,242492250,252191940

%N Numbers with exactly 8 distinct prime divisors {2,3,5,7,11,13,17,19}.

%C Successive numbers k such that EulerPhi(x)/x = m:

%C ( Family of sequences for successive n primes )

%C m=1/2 numbers with exactly 1 distinct prime divisor {2} see A000079

%C m=1/3 numbers with exactly 2 distinct prime divisors {2,3} see A033845

%C m=4/15 numbers with exactly 3 distinct prime divisors {2,3,5} see A143207

%C m=8/35 numbers with exactly 4 distinct prime divisors {2,3,5,7} see A147571

%C m=16/77 numbers with exactly 5 distinct prime divisors {2,3,5,7,11} see A147572

%C m=192/1001 numbers with exactly 6 distinct prime divisors {2,3,5,7,11,13} see A147573

%C m=3072/17017 numbers with exactly 7 distinct prime divisors {2,3,5,7,11,13,17} see A147574

%C m=55296/323323 numbers with exactly 8 distinct prime divisors {2,3,5,7,11,13,17,19} see A147575

%H Amiram Eldar, <a href="/A147575/b147575.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = 9699690 * A080682(n). - _Amiram Eldar_, Mar 10 2020

%F Sum_{n>=1} 1/a(n) = 1/1658880. - _Amiram Eldar_, Nov 12 2020

%t a = {}; Do[If[EulerPhi[9699690 x] == 1658880 x, AppendTo[a, 9699690 x]], {x, 1, 100}]; a

%Y Cf. A060735, A080682, A143207, A147571-A147575, A147576-A147580.

%K nonn

%O 1,1

%A _Artur Jasinski_, Nov 07 2008

%E More terms from _Amiram Eldar_, Mar 10 2020