Cyclic prime numbers: new class of prime numbers I have found accidentally
This article is meant to demonstrate new class of prime numbers — cyclic prime numbers, that can be derived from any prime number at certain numeric systems. Cyclic prime numbers are also related to the cyclic numbers and full reptend prime numbers.
- Introduction
First publication related to cyclic numbers and full reptend prime numbers appears in the book [1].
This book was published 200 years before this work, authors of this book show that periodic fraction derived from 1/P can be presented as converging geometric series. Authors don’t use the term geometric series, but they show that 1/7 is the sum of decreasing rational numbers.
In the book [2] there is formulation of a condition under which full reptend prime numbers appear.
In book [3] there is a mentioning of cyclic numbers and their relation to repunits.
In the book [4] there is a mentioning of divisions during the formation of periodic fractions, which are subsequently used in the formula of geometric series.
In the above mentioned books, and throughout the Internet I wasn’t able to find all the regularities hat I came up with, so I wish to share them in this article.
2. Cyclic numbers
A cyclic number is an integer in which cyclic permutations of the digits are successive integer multiples of the number.
The most famous cyclic number is 142857. It is popularized with pseudoscientic theory of an ‘enneagram’, however there are not so many scientific results can be found about it. Let’s take a look at its cyclic property:
142857 * 2 = 285714
142857 * 3 = 428571
142857 * 4 = 571428
142857 * 5 = 714285
142857 * 6 = 857142
As we can see, when the original number 142857 is multiplied by the numbers from 2 to 6, we get cyclic permutations of the number 142857.
Those numbers have other properties, for example regularities that can be observed when multiplying by numbers greater than 7, but they are not a subject of this article.
3. Cyclic prime numbers
A cyclic prime is a prime number formed from a sequence of digits in a cyclic number that repeats for more than one cycle.
The first cyclic prime formed from 142857 is 1428571, which is a prime number. Such a number can be written by the first digit of the initial cyclic number and the total number of digits. For example, for 1428571, the first digit is 1 and the total number of digits is 7.
Here are all the primes formed from the cyclic number 142857, and not exceeding titanic primes (up to 10 thousand digits). The first numbers are written in full, the longer ones described by the first digit and the number of digits.
The first 7 cyclic primes, formed from 142857: 1428571, 71428571, 7142857142857, 57142857142857,1428571428571428571428571, 28571428571428571428571428571, 7142857142857142857142857142857.
Amount of digits in those numbers: 7, 8, 13, 15, 25, 29, 31.
In total there are 23 cyclic primes, that are not greater than 10^1000.
4. Properties of prime numbers dependent on numeric system. Full reptend prime numbers
In order to consider how do cyclic primes appear, we also need to consider how cyclic numbers appear.
There is a class of prime numbers called full reptend prime. This class of prime numbers depends on the numeric system, so any prime number is a full reptend at certain numeric system.
P is a prime number. If the periodic fraction formed during the calculation of the rational number 1 / P, has a period equal to P-1 in some numeric system N, then we can say that the prime number P in the numeric system N is full reptend.
If the number P is a full reptend in some numeric system N, then all P-1 of its digits form a cyclic number. Consider a prime number P = 7 in decimal notation. The number formed from 1 / 7 = 0.(142857). The period is 6, which is equal to P-1.
Consider the remaining fractions from the set 1 / P .. P-1 / P:
2 / 7 = 0:285714
3 / 7 = 0:428571
4 / 7 = 0:571428
5 / 7 = 0:714285
6 / 7 = 0:857142
We observe that those fractions have the property of a cyclic permutation.
One of the visualizations will be presented below. In the table below, each row is a prime number.
Each column represents a numeric system. The value in a cell is the length of the period of the rational 1 / P. Highlighted in the green cells that are full reptend. First, let’s take a look at the individual parts of this table. For each prime number P, there is a sequence of possible period lengths of the fraction 1 / P.
For P = 2, the numeric system cycle length is 2. For P = 3, the numeric system cycle length is 3, etc. To calculate the length of a period in a certain numeric system, which is represented as base — we need to solve the equation:
!!! picture wanted
If the base is coprime to the P then Fermat’s little theorem says that Fermat quotient is an integer. If the base is also a generator of multiplucative group of integers modulo p, then Fermat quotient will be cyclic number, and p will be a full reptend prime.
Let’s take a look at the figure 2 for different P in different numeric systems. In the decimal system, we see that the rst prime numbers, which are full reptends, are: 7, 17, 19, 23, 29.
The numbers 2 and 5 do not have a period here, since the base of the numeric system is divisible by both of these prime numbers without remainder.
In the case of P = 3, we get a periodic fraction with a unit length of the period in the decimal system: 1/3 = 0,(3). In the case of P = 11, we get a periodic fraction with a period length of 2 in decimal: 1/11 = 0, (09).
With P = 13 we get a special case, the period length is 6, which is not equal to P-1. However, the period length is (P-1) / 2. When this proportion is respected, two sets of cyclic numbers are formed. Such P is called the 2nd reptend level prime.
Here’s the example of 2nd reptend level prime:
1/13 = 0.(076923)
2/ 13 = 0.(153846)
All other fractions from P = 13 up to P-1 / P will have the same digits as 1/13 or 2/13, but with cyclic permutations.
3/13 = 0.(230769)
4/13 = 0.(307692)
5/13 = 0.(384615)
6/13 = 0.(461538)
7/13 = 0.(538461)
8/13 = 0.(615384)
9/13 = 0.(692307)
10/13 = 0.(769230)
11/13 = 0.(846153)
12/13 = 0.(923076)
N-reptend prime numbers also form cyclic primes: primes can be formed from each of the sequences of cyclic numbers.
There are prime numbers for the first cycle: 769230769, 769230769230769230769. But also there is a prime number from the second cycle: 1538461.
Concluding this topic it is interesting to note that the numeric systems in which we meet full reptend primes are also unusual.
For P = 7, the first 2 numeric systems, in which it is a full reptend, are systems with N 3 and 5 — twin primes. Further, these positions are repeated every 7 numeric systems, and always remain in same distance. When the sum of the bases of the numeric systems is evenly divisible by 12, we meet twin primes again. For example, 17 and 19, 59 and 61.
5. Further reading
If you are interesting in the theme you can read a complete article with lots of formulas, or play with visualization code on github:
By the way, right now I’m in the process of searching endorser for arxiv.org, if anyone can give me endorsement for the Number Theory field — please contact me, I would be very graceful!
Thank you for you attention!
