login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A165781 a(n) = (2^A002326(n)-1)/(2*n+1). 7
1, 1, 3, 1, 7, 93, 315, 1, 15, 13797, 3, 89, 41943, 9709, 9256395, 1, 31, 117, 1857283155, 105, 25575, 381, 91, 178481, 42799, 5, 84973577874915, 19065, 4599, 4885260612740877, 18900352534538475, 1, 63, 1101298153654301589 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

a(n) = 1 <=> n is in A000225 <=> n = 2^k - 1 with k = 0, 1, 2, ... - M. F. Hasler, Sep 20 2017

LINKS

Robert Israel, Table of n, a(n) for n = 0..1672

MAPLE

A002326 := proc(n) if n = 0 then 1 ; else numtheory[order](2, 2*n+1) ; end if ; end proc:

A165781 := proc(n) (2^A002326(n)-1)/(2*n+1) ; end proc:

seq(A165781(n), n=0..60) ; # R. J. Mathar, Nov 16 2009

MATHEMATICA

a[n_] := (2^MultiplicativeOrder[2, 2n+1]-1)/(2n+1);

a /@ Range[0, 40] (* Jean-François Alcover, Jun 04 2020 *)

PROG

(PARI) a(n)=(2^znorder(Mod(2, n=2*n+1))-1)/n \\ M. F. Hasler, Sep 20 2017

CROSSREFS

Cf. A002326, A053446, A000225.

Sequence in context: A346784 A060487 A285020 * A152095 A096797 A084246

Adjacent sequences: A165778 A165779 A165780 * A165782 A165783 A165784

KEYWORD

easy,nonn

AUTHOR

Ctibor O. Zizka, Sep 26 2009

EXTENSIONS

Sign in definition and offset corrected by R. J. Mathar, Nov 16 2009

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 29 03:18 EST 2022. Contains 358422 sequences. (Running on oeis4.)