A069927 - OEIS

%I #13 Aug 15 2021 16:09:26

%S 3,5,9,21,45,63,85,105,117,273,285,357,585,627,765,1365,1397,1449,

%T 1677,1989,2337,3597,3705,3885,4221,4365,4485,4797,4953,5061,5607,

%U 5797,7137,7521,7565,7665,8109,10197,10545,10845,11445,11565,12597,13065,13717

%N Numbers k that divide 2^(k+3) - 1.

%H Harvey P. Dale, <a href="/A069927/b069927.txt">Table of n, a(n) for n = 1..500</a>

%t Select[Range[15000],PowerMod[2,#+3,#]==1&] (* _Harvey P. Dale_, Jul 09 2018 *)

%K easy,nonn

%O 1,1

%A _Benoit Cloitre_, Apr 25 2002