login
A124516
a(n) = least k such that 2^i*k-1 is prime for 1<=i<=n.
9
2, 2, 3, 3, 45, 45, 561330, 9549960, 42932385, 13044904290, 277344139215, 277344139215, 2045466215756535
OFFSET
1,1
MATHEMATICA
k = 1; Do[If[n < 5, inc = 1, inc = 15]; If[Mod[k, inc] > 0, k = k + inc - Mod[k, inc]]; While[Nand @@ PrimeQ[Table[2^j, {j, n}]*k - 1], k += inc]; Print[k], {n, 1, 10}] (* Ray Chandler *)
KEYWORD
nonn,more
AUTHOR
Artur Jasinski, Nov 04 2006
EXTENSIONS
Definition corrected and a(10) calculated by Farideh Firoozbakht, Nov 24 2006
a(11)-a(13) from Giovanni Resta, Apr 22 2019
STATUS
approved