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

 

Logo

The OEIS is looking to hire part-time people to help edit core sequences, upload scanned documents, process citations, fix broken links, etc. - Neil Sloane, njasloane@gmail.com

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A070528 Number of divisors of 10^n-1 (999...999 with n digits). 5
3, 6, 8, 12, 12, 64, 12, 48, 20, 48, 12, 256, 24, 48, 128, 192, 12, 640, 6, 384, 256, 288, 6, 2048, 96, 192, 96, 768, 96, 16384, 24, 6144, 128, 192, 384, 5120, 24, 24, 128, 6144, 48, 49152, 48, 4608, 1280, 192, 12, 16384, 48, 3072, 512, 1536, 48, 12288, 768 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Ray Chandler, Table of n, a(n) for n = 1..322 (first 280 terms from Hans Havermann)

FORMULA

a(n) = A000005(A002283(n)).

a(n) = Sum_{d|n} A059892(d).

a(n) = A070529(n)*(A007949(n)+3)/(A007949(n)+1).

EXAMPLE

a(7)=12 since the divisors of 9999999 are 1, 3, 9, 239, 717, 2151, 4649, 13947, 41841, 1111111, 3333333, 9999999.

MATHEMATICA

DivisorSigma[0, #]&/@(10^Range[60]-1) (* Harvey P. Dale, Jan 14 2011 *)

Table[DivisorSigma[0, 10^n - 1], {n, 60}] (* T. D. Noe, Aug 18 2011 *)

PROG

(PARI) a(n) = numdiv(10^n - 1); \\ Michel Marcus, Sep 08 2015

CROSSREFS

Cf. A018282, A018766, A027894, A027893, A027892, A027891, A027890, A027889, A027895.

Sequence in context: A233541 A077148 A246456 * A243117 A122116 A209885

Adjacent sequences:  A070525 A070526 A070527 * A070529 A070530 A070531

KEYWORD

base,nonn

AUTHOR

Henry Bottomley, May 02 2002

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified May 26 18:58 EDT 2017. Contains 287129 sequences.