login

Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.

Integers k such that 2^k == 7 (mod k).
19

%I #25 Sep 30 2018 03:13:08

%S 1,5,25,1727,3830879,33554425,19584403931,25086500333,23476467919565,

%T 4463061944990945

%N Integers k such that 2^k == 7 (mod k).

%C A larger term: 15237454403219419167053498809.

%t m = 7; Join[Select[Range[m], Divisible[2^# - m, #] &],

%t Select[Range[m + 1, 10^7], PowerMod[2, #, #] == m &]] (* _Robert Price_, Sep 26 2018 *)

%o (PARI) isok(n) = Mod(2, n)^n == 7; \\ _Michel Marcus_, Sep 27 2018

%K nonn,more

%O 1,2

%A Joe K. Crump (joecr(AT)carolina.rr.com)

%E Terms 1, 5 prepended by _Max Alekseyev_, May 18 2011

%E a(9) added by _Max Alekseyev_, May 21 2011

%E a(10) from _Max Alekseyev_, Jun 17 2012