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

1, 194997, 1463649, 1957025, 4657005, 6464145, 17214725, 70930629, 76938345, 319359365, 336837501, 429872625, 486213525, 1343289717, 1831683645, 2163016845, 2430979425, 2950546137, 3463374005, 5031564525, 5608791441, 8993704797, 9596401485, 12556945401, 13492461125, 14559291285, 18429009725

Offset

1,2

Links

Table of n, a(n) for n=1..27.

Example

1 is in this sequence because (2^1 + 1)/(2*1 - 1) = 3.

Mathematica

Select[Range[200000], IntegerQ[(2^# + 1) / (2 # - 1)] &] (* Vincenzo Librandi, Nov 20 2014 *)

Prog

(Magma) [n: n in [1..2000000] | Denominator((2^n + 1)/(2*n - 1)) eq 1];
(PARI) is(n)=Mod(2, 2*n-1)^n==-1 \\ Charles R Greathouse IV, Nov 20 2014

Crossrefs

Cf. A081856, A081858, A247094.

Sequence in context: A206052 A237088 A172790 * A069305 A129486 A203047

Adjacent sequences: A247129 A247130 A247131 * A247133 A247134 A247135

Keyword

nonn

Author

Juri-Stepan Gerasimov, Nov 20 2014

Extensions

a(5)-a(27) from Charles R Greathouse IV, Nov 20 2014

Status

approved