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%I #11 Sep 25 2018 04:01:10
%S 1,7,217,1057,3937,10447,24601,32767,91657,145337,279527,666967,
%T 1412113,2484247,2874847,3124327,4169137,4472167,9526207,12021439,
%U 16539337,16646017,19384207,20139367,24639727,28127137,28940887,30583087,66131279,68068777,70694167,72299857,72903847,73498471,87507049
%N Numbers k such that k divides 2^(2*k+1) - 1.
%C Sequence is infinite because 2^A187787(t) - 1 is a term for all t >= 1.
%t Select[Range[10^5], Mod[2^(2 # + 1) - 1, #] == 0 &] (* _Michael De Vlieger_, Sep 24 2018 *)
%o (PARI) isok(n) = Mod(2, n)^(2*n+1)==1;
%Y Cf. A187787, A296369, A319222.
%K nonn
%O 1,2
%A _Altug Alkan_, Sep 22 2018
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