cp's OEIS Frontend

A247132 Numbers k such that 2k - 1 divides 2^k + 1.

%I A247132 #21 Jun 27 2024 22:21:37
%S A247132 1,194997,1463649,1957025,4657005,6464145,17214725,70930629,76938345,
%T A247132 319359365,336837501,429872625,486213525,1343289717,1831683645,
%U A247132 2163016845,2430979425,2950546137,3463374005,5031564525,5608791441,8993704797,9596401485,12556945401,13492461125,14559291285,18429009725
%N A247132 Numbers k such that 2k - 1 divides 2^k + 1.
%e A247132 1 is in this sequence because (2^1 + 1)/(2*1 - 1) = 3.
%t A247132 Select[Range[200000], IntegerQ[(2^# + 1) / (2 # - 1)] &] (* _Vincenzo Librandi_, Nov 20 2014 *)
%o A247132 (Magma) [n: n in [1..2000000] | Denominator((2^n + 1)/(2*n - 1)) eq 1];
%o A247132 (PARI) is(n)=Mod(2,2*n-1)^n==-1 \\ _Charles R Greathouse IV_, Nov 20 2014
%Y A247132 Cf. A081856, A081858, A247094.
%K A247132 nonn
%O A247132 1,2
%A A247132 _Juri-Stepan Gerasimov_, Nov 20 2014
%E A247132 a(5)-a(27) from _Charles R Greathouse IV_, Nov 20 2014