OFFSET
1,5
COMMENTS
a(n) is the number of positive integers which are coprime to n minus the number of distinct primes dividing n.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..10000
Peter Luschny, Blog on OEIS, Euler's totient function
FORMULA
a(n) = phi(n) - omega(n), by definition.
EXAMPLE
a(7) = phi(7) - omega(7) = card({1,2,3,4,5,6}) - card({7}) = 6 - 1 = 5
MAPLE
with(numtheory): a := n -> phi(n) - nops(factorset(n));
MATHEMATICA
Table[EulerPhi[n] - PrimeNu[n], {n, 1, 50}] (* G. C. Greubel, Apr 23 2017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Peter Luschny, Jun 30 2010
STATUS
approved