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

1,2

Comments

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

Links

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

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 *)

Crossrefs

Cf. A210651.

Sequence in context: A029606 A247283 A050595 * A177941 A029667 A264747

Adjacent sequences: A182026 A182027 A182028 * A182030 A182031 A182032

Keyword

nonn

Author

Pierre CAMI, Apr 07 2012

Status

approved