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!)
A084681 Order of 10 modulo 9n [i.e., least m such that 10^m = 1 (mod 9n)] or 0 when no such number exists. 4
1, 0, 3, 0, 0, 0, 6, 0, 9, 0, 2, 0, 6, 0, 0, 0, 16, 0, 18, 0, 6, 0, 22, 0, 0, 0, 27, 0, 28, 0, 15, 0, 6, 0, 0, 0, 3, 0, 6, 0, 5, 0, 21, 0, 0, 0, 46, 0, 42, 0, 48, 0, 13, 0, 0, 0, 18, 0, 58, 0, 60, 0, 18, 0, 0, 0, 33, 0, 66, 0, 35, 0, 8, 0, 0, 0, 6, 0, 13, 0, 81, 0, 41, 0, 0, 0, 84, 0, 44, 0, 6, 0, 15, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

K. Matthews, Finding the order of a (mod m)

FORMULA

From Robert Israel, Feb 22 2019: (Start)

a(n) = A084680(9*n).

If n is not divisible by 3, a(n) = A084680(n).

Otherwise a(n) can be either A084680(n), 3*A084680(n) or 9*A084680(n). (End)

MAPLE

f:= proc(n)

if igcd(n, 10)>1 then 0 else numtheory:-order(10, 9*n) fi

end proc:

map(f, [$1..100]); # Robert Israel, Feb 22 2019

MATHEMATICA

a[n_] := If[GCD[10, 9n] != 1, 0, MultiplicativeOrder[10, 9n]];

Array[a, 100] (* Jean-François Alcover, Jul 19 2020 *)

PROG

(PARI) a(n) = if (gcd(10, 9*n) != 1, 0, znorder(Mod(10, 9*n))); \\ Michel Marcus, Feb 23 2019

(GAP) List([1..100], n->OrderMod(10, 9*n)); # Muniru A Asiru, Feb 26 2019

CROSSREFS

Cf. A084680, A190301, A216479.

Sequence in context: A181189 A327889 A221702 * A261038 A285852 A096528

Adjacent sequences: A084678 A084679 A084680 * A084682 A084683 A084684

KEYWORD

nonn

AUTHOR

Lekraj Beedassy, Jun 30 2003

EXTENSIONS

More terms from John W. Layman, Oct 09 2003

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 26 21:15 EST 2022. Contains 358362 sequences. (Running on oeis4.)