A046809 - OEIS

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

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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

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

KEYWORD

hard,nonn

AUTHOR

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

EXTENSIONS

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

STATUS

approved