login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A064126 Number of divisors of 10^n - 1 that are relatively prime to 10^m - 1 for all 0 < m < n. 0
3, 2, 2, 2, 4, 4, 4, 4, 2, 2, 4, 2, 8, 2, 4, 4, 4, 4, 2, 4, 8, 8, 2, 2, 8, 4, 4, 8, 32, 8, 8, 32, 4, 8, 8, 2, 8, 2, 2, 4, 16, 8, 16, 8, 4, 16, 4, 2, 4, 8, 16, 4, 16, 4, 16, 4, 8, 4, 4, 8, 128, 2, 32, 16, 4, 4, 8, 8, 8, 4, 4, 8, 8, 8, 8, 4, 16, 16, 64, 4, 32, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..82.

Sam Wagstaff, Cunningham Project, Factorizations of 10^n-1, n odd, n<300

MATHEMATICA

a = {1}; Do[ d = Divisors[ 10^n - 1 ]; l = Length[ d ]; c = 0; k = 1; While[ k < l + 1, If[ Union[ GCD[ a, d[ [ k ] ] ] ] == {1}, c++ ]; k++ ]; Print[ c ]; a = Union[ Flatten[ Append[ a, Transpose[ FactorInteger[ 10^n - 1 ] ][ [ 1 ] ] ] ] ], {n, 1, 61} ]

PROG

(PARI) a(n) = sumdiv(10^n-1, d, vecsum(vector(n-1, k, gcd(d, 10^k-1) == 1)) == n-1); \\ Michel Marcus, Jun 23 2018

CROSSREFS

Cf. A063982.

Sequence in context: A064123 A024703 A102845 * A175333 A130845 A134653

Adjacent sequences:  A064123 A064124 A064125 * A064127 A064128 A064129

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Sep 10 2001

EXTENSIONS

a(62)-a(82) from Giovanni Resta, Jun 26 2018

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 29 01:40 EST 2020. Contains 331328 sequences. (Running on oeis4.)