OFFSET
1,1
COMMENTS
Since, as Euler proved, the random chance of two integers not having a common prime factor is 6/Pi^2, these are the odd integers that share common factors with an above average fraction of integers. Is it known, or can it be calculated, what portion of odd integers satisfy this condition? (All even numbers qualify; for all multiples of 2, phi(n)/n <= 0.5.)
The sequence is closed under multiplication by any odd number. If we include the even numbers, the sequence of primitive terms begins 2, 15, 21, 33, 663, ... . - Peter Munn, Apr 11 2021
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
EXAMPLE
phi(33)/33 = 20/33 or 0.6060606...; 6/Pi^2 is 0.6079271....
PROG
(PARI) is(n)=n%2 && eulerphi(n)/n<6/Pi^2 \\ Charles R Greathouse IV, Sep 13 2013
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Matthew Vandermast, Feb 19 2003
STATUS
approved