A098466 - OEIS

%I #26 Apr 07 2023 08:57:22

%S 86,146,806,5010,19338,20210,67278,83406

%N Numbers k such that N*2^k - 1 is prime where N = 9999999999999999999999988888888888888888887777777777777777766666666666665555555555544444443333322211.

%C 9999999999999999999999988888888888888888887777777777777777766666666666665555555555544444443333322211 is a 100-digit prime that is easy to remember: 23 9's then 19 8's then 17 7's then 13 6's then 11 5's then 7 4's then 5 3's then 3 2's and 2 1's. Writing p(k) for prime(k), this is p(9)9 p(8)8 p(7)7 p(6)6 p(5)5 p(4)4 p(3)3 p(2)2 p(1)1.

%C Same number can be shortened as (10^100-(10^77+10^58+10^41+10^28+10^17+10^10+10^5-7)/9-12). (By David A. Corneth, original comment can be found in A098467)

%C a(7) > 22200. - _Jinyuan Wang_, Mar 19 2020

%C a(8) > 71000. - _Daniel Suteu_, Sep 04 2020

%Y Cf. A098467.

%K nonn,more,less

%O 1,1

%A _Pierre CAMI_, Sep 09 2004

%E a(5)-a(6) from _Jinyuan Wang_, Mar 19 2020

%E a(7) from _Daniel Suteu_, Sep 04 2020

%E a(8) from _Michael S. Branicky_, Apr 06 2023