A084295 n is such that pi(n*prime(n))/n is an integer.

1, 3, 47, 88, 200, 547, 12182, 15335, 39104, 58122, 73282, 150740, 480886

Offset: 1

Author

Labos Elemer, May 27 2003

Keywords

• nonn
• hard
• more

Comments

a(9) > 30000. - Michel Marcus, Sep 02 2019

a(13) > 200000. - Giovanni Resta, Sep 02 2019

Crossrefs

Cf. A000040, A000720, A033286, A057855, A084297, A084298.

Programs

Mathematica

Do[s=PrimePi[n*Prime[n]]/n; If[IntegerQ[s], Print[n]], {n, 1, 100000}]
Select[Range[16000],IntegerQ[PrimePi[#*Prime[#]]/#]&] (* Harvey P. Dale, Jul 23 2015 *)

PARI

isok(n) = denominator(primepi(n*prime(n))/n) == 1; \\ Michel Marcus, Sep 02 2019

Extensions

Corrected by Harvey P. Dale, Jul 23 2015

a(9)-a(12) from Giovanni Resta, Sep 02 2019

a(13) from Chai Wah Wu, May 14 2020