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%I #26 Sep 06 2021 19:13:09
%S 1,3,19147,129505699483,674344345281,1643434407157,5675297754009,
%T 12174063716147,162466075477787,313255455573801,324082741109271
%N Numbers k such that 2^k == 5 (mod k).
%H Joe K. Crump, <a href="https://web.archive.org/web/20120104074313/http://www.immortaltheory.com/NumberTheory/2nmodn.htm">2^n mod n</a>
%H OEIS Wiki, <a href="/wiki/2^n mod n">2^n mod n</a>
%t m = 5; Join[Select[Range[m], Divisible[2^# - m, #] &],
%t Select[Range[m + 1, 10^6], PowerMod[2, #, #] == m &]] (* _Robert Price_, Oct 08 2018 *)
%Y Cf. A015910, A036236, A050259 (numbers k such that 2^k == 3 (mod k)), A033981, A051447, A033982, A051446, A033983, A128122, A128123, A128124, A128125, A128126.
%K hard,more,nonn
%O 1,2
%A _Alexander Adamchuk_, Feb 15 2007
%E 1 and 3 added by _N. J. A. Sloane_, Apr 23 2007
%E Missing a(10) inserted by _Sergey Paramonov_, Sep 06 2021