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%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