A147572 Numbers with exactly 5 distinct prime divisors {2,3,5,7,11}.

2310, 4620, 6930, 9240, 11550, 13860, 16170, 18480, 20790, 23100, 25410, 27720, 32340, 34650, 36960, 41580, 46200, 48510, 50820, 55440, 57750, 62370, 64680, 69300, 73920, 76230, 80850, 83160, 92400, 97020, 101640, 103950, 110880, 113190, 115500, 124740, 127050

Offset

1,1

Comments

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

( Family of sequences for successive n primes )

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

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

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

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

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

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

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

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

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Formula

a(n) = 2310 * A051038(n). - Amiram Eldar, Mar 10 2020

Sum_{n>=1} 1/a(n) = 1/480. - Amiram Eldar, Nov 12 2020

Mathematica

a = {}; Do[If[EulerPhi[x]/x == 16/77, AppendTo[a, x]], {x, 1, 100000}]; a
Select[Range[130000], FactorInteger[#][[All, 1]]=={2, 3, 5, 7, 11}&] (* Harvey P. Dale, Oct 04 2020 *)

Crossrefs

Cf. A051038, A060735, A143207, A147571-A147575, A147576-A147580.

Sequence in context: A258360 A076252 A264718 * A046303 A046403 A288072

Adjacent sequences: A147569 A147570 A147571 * A147573 A147574 A147575

Keyword

nonn

Author

Artur Jasinski, Nov 07 2008

Extensions

More terms from Amiram Eldar, Mar 10 2020

Status

approved