A182029 Least odd k > a(n-1) such that 3*k*2^n-1 is a prime number.

1, 5, 7, 9, 15, 25, 31, 33, 35, 45, 47, 49, 59, 65, 91, 115, 127, 135, 137, 149, 165, 175, 183, 185, 217, 225, 245, 273, 279, 287, 303, 349, 359, 429, 433, 445, 457, 525, 577, 593, 599, 629, 641, 673, 675, 679, 727, 749, 775, 795, 835, 855, 973, 1049, 1087

Offset: 1

Author

Pierre CAMI, Apr 07 2012

Keywords

• nonn

Comments

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

Links

• Pierre CAMI, Table of n, a(n) for n = 1..5000

Crossrefs

Cf. A210651.

Programs

Mathematica

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 *)