login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual Appeal: Please make a donation to keep the OEIS running. In 2018 we replaced the server with a faster one, added 20000 new sequences, and reached 7000 citations (often saying "discovered thanks to the OEIS").
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A015919 Positive integers n such that 2^n == 2 (mod n). 27
1, 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337, 341, 347, 349, 353, 359, 367 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Includes 341 which is first pseudoprime to base 2 and distinguishes sequence from A008578.

First composite even term is a(14868) = 161038 = A006935(2). - Max Alekseyev, Feb 11 2015

If n is a term, then so is 2^n - 1. - Max Alekseyev, Sep 22 2016

Terms of the form 2^k - 2 corresponds to k in A296104. - Max Alekseyev, Dec 04 2017

If 2^n-1 is a term, then so is n. - Thomas Ordowski, Apr 27 2018

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..20000

FORMULA

A015919 = {1} U A000040 U A001567 U A006935 = A001567 U A006935 U A008578. - Ray Chandler, Dec 07 2003; corrected by Max Alekseyev, Feb 11 2015

MATHEMATICA

Prepend[ Select[ Range@370, PowerMod[2, #, #] == 2 &], {1, 2}] // Flatten (* Robert G. Wilson v, May 16 2018 *)

PROG

(PARI) is(n)=Mod(2, n)^n==2 \\ Charles R Greathouse IV, Mar 11 2014

CROSSREFS

Contains A002997 as a subsequence.

The odd terms form A176997.

Cf. A000040, A001567, A008578.

Sequence in context: A216886 A273960 A100726 * A064555 A216887 A095320

Adjacent sequences:  A015916 A015917 A015918 * A015920 A015921 A015922

KEYWORD

nonn

AUTHOR

Robert G. Wilson v

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 18 21:01 EST 2018. Contains 318245 sequences. (Running on oeis4.)