A046808 Recursive sequence of indices of Proth primes a*2^b + 1.

1, 2, 3, 5, 7, 14, 19, 46, 48, 62, 67, 74, 81, 89, 589, 2090, 2299, 7742, 1925975, 1989191

Offset

0,2

Comments

Searched up to 7742*2^100000 + 1 (3871*2^100001 + 1 is the format in the Yves Gallot's Proth Program)

Links

Table of n, a(n) for n=0..19.

Chris K. Caldwell, The Prime Pages, 3871*2^1925976+1 (7742*2^1925975+1)

Chris K. Caldwell, The Prime Pages, 1925975*2^1989191+1

Y. Gallot, Proth.exe: Windows Program for Finding Large Primes

Formula

a(n) = least integer b greater than a(n-1) such that a(n-1)*2^b + 1 is prime

Mathematica

t = {a = 1}; Do[If[PrimeQ[a*2^n + 1], AppendTo[t, a = n]], {n, 2, 2300}]; t (* Jayanta Basu, Jun 29 2013 *)

Crossrefs

Sequence in context: A279953 A260523 A114625 * A097799 A005629 A028304

Adjacent sequences: A046805 A046806 A046807 * A046809 A046810 A046811

Keyword

hard,nonn,more

Author

Chad Davis (cad16(AT)po.cwru.edu)

Extensions

a(18) from Kellen Shenton, May 08 2022

a(19) from Kellen Shenton, May 14 2022

Status

approved