OFFSET
1,1
COMMENTS
1/a(n) is the fraction of primes in the reduced residue system mod A307712(n).
LINKS
Robert Israel, Table of n, a(n) for n = 1..600
EXAMPLE
a(3) = 2 because A307712(3) = 5 and 1/2 of the reduced residue system mod 5 are primes.
MAPLE
g:= proc(n) uses numtheory;
local v;
v:= phi(n)/(pi(n) - nops(factorset(n)));
if v::integer then v fi;
end proc:
map(g, [$3..40000]);
MATHEMATICA
Select[Table[EulerPhi[n]/Count[Prime@ Range@ PrimePi@ n, _?(GCD[#, n] == 1 &)], {n, 3, 25000}], IntegerQ] (* Michael De Vlieger, Apr 23 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert Israel, Apr 23 2019
STATUS
approved