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

 

Logo

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A122783 Nonprimes n such that 6^n==6 (mod n). 3
1, 6, 10, 15, 21, 30, 35, 105, 185, 190, 217, 231, 301, 430, 435, 481, 561, 777, 1105, 1111, 1221, 1261, 1333, 1729, 1866, 2121, 2465, 2553, 2701, 2821, 2955, 3421, 3565, 3589, 3885, 3913, 4123, 4495, 5061, 5565, 5662, 5713, 6531, 6533, 6601 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Theorem: If both numbers q and 2q-1 are primes then n=q*(2q-1) is in the sequence iff q<5 or q is of the form 12k+1. 6,15,2701,18721,49141,104653,226801,665281,... are such terms.

LINKS

Table of n, a(n) for n=1..45.

MATHEMATICA

Select[Range[7000], ! PrimeQ[ # ] && Mod[6^#, # ] == Mod[6, # ] &]

CROSSREFS

Cf. A005937.

Sequence in context: A115744 A211007 A315279 * A124000 A229321 A229323

Adjacent sequences:  A122780 A122781 A122782 * A122784 A122785 A122786

KEYWORD

easy,nonn

AUTHOR

Farideh Firoozbakht, Sep 12 2006

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 January 17 14:12 EST 2019. Contains 319225 sequences. (Running on oeis4.)