A046809 Recursive sequence of indices of Proth primes a*2^b - 1.

1, 2, 4, 5, 8, 10, 11, 26, 286, 365, 602, 630, 713, 808, 1327, 3561, 3566, 5286, 5477, 10600, 13485, 15441, 17339, 76856, 277718, 279098, 977278

Offset

1,2

Comments

Searched up to 76856*2^100000 - 1 (9607*2^100003 - 1 is the format in the Yves Gallot's Proth Program)

Links

Table of n, a(n) for n=1..27.

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

Formula

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

Prog

(PARI) a=1; until(, print1(a, ", "); for(b=a+1, +oo, if(ispseudoprime(a*2^b-1), a=b; break()))) \\ Jeppe Stig Nielsen, Apr 29 2022

Crossrefs

Sequence in context: A067938 A306073 A018457 * A112777 A188972 A047612

Adjacent sequences: A046806 A046807 A046808 * A046810 A046811 A046812

Keyword

hard,nonn

Author

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

Extensions

a(25)-a(27) from Kellen Shenton Apr 29 2022

Status

approved