A177691 - OEIS

%I #8 Feb 13 2019 16:34:07

%S 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,

%T 17,17,19,19,19,19,21,21,21,21,21,21,23,23,23,23,23,23,25,25,25,25,27,

%U 27,27,27,29,29,29,29,31,31,31,31,33,33,35,35,37,37,37,37,37,37,39,39,39

%N The odd values of PrimePi(.), with repetition.

%H Robert Israel, <a href="/A177691/b177691.txt">Table of n, a(n) for n = 1..10000</a>

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

%p seq((2*n-1)$(ithprime(2*n)-ithprime(2*n-1)),n=1..30); # _Robert Israel_, Feb 13 2019

%t Select[PrimePi[Range[300]],OddQ] (* _Harvey P. Dale_, Dec 24 2014 *)

%Y Cf. A000720, A005408.

%K nonn,easy

%O 1,2

%A _Giovanni Teofilatto_, May 11 2010

%E Erroneous formula removed by _R. J. Mathar_, May 14 2010