A157966 - OEIS

%I #15 Apr 25 2024 23:59:45

%S 0,1,1,1,3,3,5,5,7,9,9,11,13,13,15,17,19,19,21,23,23,25,27,29,31,33,

%T 33,35,35,37,41,43,45,45,49,49,51,53,55,57,59,59,63,63,65,65,69,73,75,

%U 75,77,79,79,83,85,87,89,89,91,93,93,97,101,103,103,105,109,111,115,115,117

%N Number of 3's in A157733(n).

%C Odd numbers missing in the sequence: 39, 47, 61, 67, 71, 81, 95, 99, 107, 113, 137, 141 etc.

%C The numbers above are essentially 2*A060461(n) - 1. - _Mikhail Kurkov_, Dec 18 2021

%F a(n) = floor((prime(n)-2)/3) for n != 2. - _Kevin Ryde_, Apr 25 2024

%o (PARI) a(n) = if(n==2,1, (prime(n)-2)\3); \\ _Kevin Ryde_, Apr 25 2024

%Y Cf. A157733, A060461.

%K nonn,easy

%O 0,5

%A _Paul Curtz_, Mar 10 2009

%E Edited and extended by _R. J. Mathar_, Mar 15 2009