A182029 - OEIS

%I #9 Sep 12 2023 16:03:56

%S 1,5,7,9,15,25,31,33,35,45,47,49,59,65,91,115,127,135,137,149,165,175,

%T 183,185,217,225,245,273,279,287,303,349,359,429,433,445,457,525,577,

%U 593,599,629,641,673,675,679,727,749,775,795,835,855,973,1049,1087

%N Least odd k > a(n-1) such that 3*k*2^n-1 is a prime number.

%C As n increases a(n)/A000217(n) tends to 0.45.

%H Pierre CAMI, <a href="/A182029/b182029.txt">Table of n, a(n) for n = 1..5000</a>

%t lok[{n_,a_}]:=Module[{k=a+2,c=3*2^n},While[!PrimeQ[c*k-1],k+=2];{n+1,k}]; Drop[NestList[ lok,{1,1},60][[;;,2]],{2}] (* _Harvey P. Dale_, Sep 12 2023 *)

%Y Cf. A210651.

%K nonn

%O 1,2

%A _Pierre CAMI_, Apr 07 2012