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A171928 Numbers k which divide the periodic part of the decimal expansion of 1/k. 3
3, 6, 487, 1461, 4383, 13149, 56598313, 169794939 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

There are two definitions of the periodic part: zeros may either begin or end the periodic part. For example, for 1/11 = 0.0909090..., the periodic part could be either 09 or 90. This sequence assumes that the zeros are at the beginning of the periodic part. See A179267 for the case of zeros at the end of the periodic part. The prime numbers in this sequence are in A045616. The three numbers following 487 are 3*487, 9*487, and 27*487. There are no other multiples of 487 here because 3 and 487 are the only prime factors of 10^486-1 that occur to a power greater than 1. - T. D. Noe, Jul 06 2010

LINKS

Table of n, a(n) for n=1..8.

Helmut Richter, Factors of 10^486-1

EXAMPLE

6 is a term because 1/6 = 0.166666... has periodic part 6, which is divisible by 6.

CROSSREFS

Cf. A045616, A179267.

Sequence in context: A126297 A157540 A179267 * A308259 A034879 A113588

Adjacent sequences:  A171925 A171926 A171927 * A171929 A171930 A171931

KEYWORD

nonn,base,more

AUTHOR

Zhining Yang, Jan 05 2010

EXTENSIONS

Example shortened by T. D. Noe, Jun 27 2010

Extended by T. D. Noe, Jul 06 2010

STATUS

approved

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Last modified August 16 16:08 EDT 2022. Contains 356169 sequences. (Running on oeis4.)