A083230 Number of repunit divisors of n.

1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1

Offset

1,11

Comments

Differs from A043284 (maximal run length in decimal expansion) from a(100) on. - M. F. Hasler, Oct 18 2019

Links

Paolo Xausa, Table of n, a(n) for n = 1..10000 (terms 1..1221 from Andrew Howroyd)

Example

n = 110, divisors are {1, 2, 5, 10, 11, 22, 55, 110} with two repunits: 1 and 11, therefore a(110) = 2.
n = 111, divisors are {1, 3, 37, 111} with two repunits: 1 and 111, therefore a(111) = 2.
n = 111111, divisors are {1, 3, 7, 11, 13, 21, 33, 37, 39, 77, 91, 111, 143, 231, 259, 273, 407, 429, 481, 777, 1001, 1221, 1443, 2849, 3003, 3367, 5291, 8547, 10101, 15873, 37037, 111111} with four repunits: 1, 11, 111 and 111111, therefore a(111111) = 4.

Mathematica

A083230[n_]:=Count[IntegerDigits[Divisors[n]], {1..}]; Array[A083230, 100] (* Paolo Xausa, Sep 27 2023 *)

Prog

(PARI) a(n)={my(s=0, k=1); while(k<=n, if(n%k==0, s++); k=10*k+1); s} \\ Andrew Howroyd, Aug 07 2018

Crossrefs

Cf. A000005, A002275, A043284.

Cf. A109492.

Sequence in context: A240228 A110503 A030556 * A043284 A030575 A350040

Adjacent sequences: A083227 A083228 A083229 * A083231 A083232 A083233

Keyword

nonn,base

Author

Reinhard Zumkeller, Jun 01 2003

Status

approved