A177691 The odd values of PrimePi(.), with repetition.

1, 3, 3, 5, 5, 7, 7, 9, 9, 9, 9, 9, 9, 11, 11, 11, 11, 11, 11, 13, 13, 15, 15, 15, 15, 15, 15, 17, 17, 19, 19, 19, 19, 21, 21, 21, 21, 21, 21, 23, 23, 23, 23, 23, 23, 25, 25, 25, 25, 27, 27, 27, 27, 29, 29, 29, 29, 31, 31, 31, 31, 33, 33, 35, 35, 37, 37, 37, 37, 37, 37, 39, 39, 39

Offset: 1

Author

Giovanni Teofilatto, May 11 2010

Keywords

• nonn
• easy

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000720, A005408.

Programs

Maple

seq((2*n-1)$(ithprime(2*n)-ithprime(2*n-1)),n=1..30); # Robert Israel, Feb 13 2019

Mathematica

Select[PrimePi[Range[300]],OddQ] (* Harvey P. Dale, Dec 24 2014 *)

Formula

Obtained by removing all even numbers from A000720. Block lengths (frequencies of repetitions) are in A078584.

Extensions

Erroneous formula removed by R. J. Mathar, May 14 2010