A085342 - OEIS

A085342

Number of primes between phi(n) and n, where n is included in the count if it is a prime, while phi(n) is never included in the count even if it is a prime.

0, 1, 1, 1, 1, 2, 1, 2, 1, 2, 1, 3, 1, 3, 2, 2, 1, 4, 1, 4, 3, 4, 1, 5, 1, 4, 2, 4, 1, 6, 1, 5, 3, 5, 2, 6, 1, 5, 3, 6, 1, 8, 1, 6, 5, 6, 1, 9, 2, 7, 4, 6, 1, 9, 4, 7, 5, 7, 1, 11, 1, 8, 7, 7, 3, 10, 1, 8, 5, 10, 1, 11, 1, 10, 9, 10, 4, 12, 1, 11, 6, 10, 1, 14, 5, 10, 7, 11, 1, 15, 4, 10, 7, 10, 4, 13, 1

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OFFSET

1,6

COMMENTS

Number of primes in (phi(n), n]. - Charles R Greathouse IV, Dec 26 2013

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..16384

FORMULA

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

a(n) = A074398(n) + A010051(n). - Antti Karttunen, Dec 16 2017

EXAMPLE

n=12: phi(n)=4, pi(12)-pi(4)=5-2=3.

MATHEMATICA

Array[PrimePi[#] - PrimePi@ EulerPhi@ # &, 97] (* Michael De Vlieger, Dec 16 2017 *)

PROG

(PARI) a(n) = primepi(n) - primepi(eulerphi(n)); \\ Michel Marcus, Dec 26 2013

CROSSREFS

Cf. A000720, A000010, A010051, A070803, A070804, A074398, A085341-A085347.

Sequence in context: A055399 A029426 A369916 * A025825 A293224 A082303

Adjacent sequences: A085339 A085340 A085341 * A085343 A085344 A085345

KEYWORD

nonn,look

AUTHOR

Labos Elemer, Jul 10 2003

EXTENSIONS

Name clarified by Antti Karttunen, Dec 16 2017

STATUS

approved