A070804 Number of primes not exceeding phi(n).

0, 0, 1, 1, 2, 1, 3, 2, 3, 2, 4, 2, 5, 3, 4, 4, 6, 3, 7, 4, 5, 4, 8, 4, 8, 5, 7, 5, 9, 4, 10, 6, 8, 6, 9, 5, 11, 7, 9, 6, 12, 5, 13, 8, 9, 8, 14, 6, 13, 8, 11, 9, 15, 7, 12, 9, 11, 9, 16, 6, 17, 10, 11, 11, 15, 8, 18, 11, 14, 9, 19, 9, 20, 11, 12, 11, 17, 9, 21, 11, 16, 12, 22, 9, 18, 13, 16

Offset

1,5

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..2000

Formula

a(n) = A000720(A000010(n)) = pi(phi(n)).

Example

n=50: phi[50]=20,Pi[20]=8=a(50)

Mathematica

Table[PrimePi[EulerPhi[n]], {n, 1, 256}]

Prog

(Magma) [#PrimesUpTo(EulerPhi(n)): n in [1..90]]; // Vincenzo Librandi, Mar 26 2017

Crossrefs

Cf. A007818, A000010, A000720, A070800, A070801, A070802, A070803.

Sequence in context: A262746 A007828 A378117 * A303429 A303656 A253630

Adjacent sequences: A070801 A070802 A070803 * A070805 A070806 A070807

Keyword

easy,nonn

Author

Labos Elemer, May 08 2002

Status

approved