

A345467


Ratios R(k)/k for which R(k) / k is an integer, where R(k) = A002275(k) is a repunit.


0




OFFSET

1,2


COMMENTS

This is the sequence where fractions of repunits (A002275) and their number of digits in base 10 R(k) / k are integers, where k is A014950(n). This happens for all k of the form k=3^m; this is true because R(3k) / R(k) = 10^(2k) + 10^n*k + 1, which is divisible by 3. Therefore R(3^m) is divisible by 3^m by induction on m. There are additional solutions in A014950.


LINKS

Table of n, a(n) for n=1..5.


FORMULA

a(n) = A002275(A014950(n))/A014950(n).


EXAMPLE

For n = 2, a(2) = 111/3 = 37. For n = 3, a(3) = 111111111/9 = 12345679.


MATHEMATICA

s = Join[{1}, Select[Range[3, 81, 6], PowerMod[10, #, #] == 1 &]]; Table[(10^n  1)/(9*n), {n, s}] (* Amiram Eldar, Jun 20 2021 *)


PROG

(Python) [(10**n1)//(9*n) for n in range(1, 300) if not (10**n1)//9 % n]


CROSSREFS

Cf. A002275, A014950.
Sequence in context: A289820 A087020 A238840 * A329226 A171407 A023930
Adjacent sequences: A345464 A345465 A345466 * A345468 A345469 A345470


KEYWORD

base,nonn


AUTHOR

Thomas T. Burgess, Jun 20 2021


STATUS

approved



