OFFSET
1,1
COMMENTS
LINKS
Robert Israel, Table of n, a(n) for n = 1..600
EXAMPLE
a(6)=9 is in the sequence because 3 of the 6 reduced residues mod 9 are prime, and 3 divides 6. The reduced residues are 1,2,4,5,7,8, of which 2,5,7 are prime.
8 is not in the sequence because 3 of the 4 reduced residues mod 8 are prime, and 3 does not divide 4.
MAPLE
filter:= proc(n) uses numtheory;
type(phi(n)/(pi(n) - nops(factorset(n))), integer);
end proc:
select(filter, [$3..10000]);
MATHEMATICA
Select[Range[3, 1500], Function[n, IntegerQ[EulerPhi[n]/Count[Prime@ Range@ PrimePi@ n, _?(GCD[#, n] == 1 &)]]]] (* Michael De Vlieger, Apr 23 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert Israel, Apr 23 2019
STATUS
approved