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Cyclic Number


A cyclic number is a positive integer represented by a block of n-1 decimal digits, with leading zeros retained, that, when multiplied by 1, 2, 3, ..., n-1, produces cyclic permutations of that block. Here n is a full reptend prime (Gil and Weiner 2008), the first few of which are 7, 17, 19, 23, 29, 47, 59, 61, 97, ... (OEIS A001913).

The decimal expansions giving the first few cyclic numbers are

1/7=0.142857^_
(1)
1/(17)=0.0588235294117647^_
(2)
1/(19)=0.052631578947368421^_
(3)
1/(23)=0.0434782608695652173913^_
(4)

The corresponding blocks, cyclically rotated to begin with their first nonzero digit, occur in OEIS A004042.

CyclicNumberFraction

The numbers of full reptend primes <=10^n for n=0, 1, 2, ... are 0, 1, 9, 60, 467, 3617, 29500, 248881, 2155288, 19016617, 170169241, ... (OEIS A086018). Artin's conjecture predicts infinitely many cyclic numbers and that the proportion of full reptend primes among all primes tends to Artin's constant C=0.3739558136.... The proportion of full reptend primes among primes <=10^(10) is approximately 0.3739552.

When a cyclic number is multiplied by its generating prime, the result is a string of 9s. By Midy's theorem, the two equal-length halves of its digit block also sum to a string of 9s (Gil and Weiner 2006).

See Yates (1973) for a table of prime period lengths for primes <1370471.


See also

Artin's Constant, Decimal Expansion, Full Reptend Prime, Midy's Theorem, Unique Prime

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References

Gardner, M. "Cyclic Numbers." Ch. 10 in Mathematical Circus: More Puzzles, Games, Paradoxes and Other Mathematical Entertainments from Scientific American. New York: Knopf, pp. 111-122, 1979.Gil, J. B. and Weiner, M. D. "On Cyclic Numbers and an Extension of Midy's Theorem." 12 May 2006. https://arxiv.org/abs/math/0605347.Gil, J. B. and Weiner, M. D. "A Quick Change of Base Algorithm for Fractions." College Math. J. 39, 56-59, 2008. https://www.jstor.org/stable/27646569.Guttman, S. "On Cyclic Numbers." Amer. Math. Monthly 41, 159-166, 1934. https://doi.org/10.2307/2302255.Kraitchik, M. "Cyclic Numbers." §3.7 in Mathematical Recreations. New York: W. W. Norton, pp. 75-76, 1942.Numberphile. "Cyclic Numbers." Oct. 27, 2013. https://www.youtube.com/watch?v=WUlaUalgxqI.Rao, K. S. "A Note on the Recurring Period of the Reciprocal of an Odd Number." Amer. Math. Monthly 62, 484-487, 1955.Rivera, C. "Problems & Puzzles: Puzzle 012-Period Length of 1/p." https://www.primepuzzles.net/puzzles/puzz_012.htm.Sloane, N. J. A. Sequences A001913/M4353, A004042, and A086018 in "The On-Line Encyclopedia of Integer Sequences."Yates, S. Primes with Given Period Length. Trondheim, Norway: Universitetsforlaget, 1973.

Referenced on Wolfram|Alpha

Cyclic Number

Cite this as:

Weisstein, Eric W. "Cyclic Number." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/CyclicNumber.html

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