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A163787 a(n) is the n-th J_7-prime (Josephus_7 prime). 2
5, 11, 21, 35, 85, 103, 161, 231, 543, 1697, 1995, 2289, 37851, 49923, 113443, 236091, 285265 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Place the numbers 1..N (N>=2) on a circle and cyclicly mark the 7th unmarked number until all N numbers are marked. The order in which the N numbers are marked defines a permutation; N is a J_7-prime if this permutation consists of a single cycle of length N.

There are 17 J_7-primes in the interval 2..1000000 only. No formula is known; the J_7-primes have been found by exhaustive search.

REFERENCES

P. R. J. Asveld, Permuting Operations on Strings-Their Permutations and Their Primes, Twente University of Technology, 2014; http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.216.1682; http://doc.utwente.nl/67513/1/pospp.pdf.

R. L. Graham, D.E. Knuth & O. Patashnik, Concrete Mathematics (1989), Addison-Wesley, Reading, MA. Sections 1.3 & 3.3.

LINKS

Table of n, a(n) for n=1..17.

P. R. J. Asveld, Permuting Operations on Strings  and Their Relation to Prime Numbers, Discrete Applied Mathematics 159 (2011) 1915-1932.

EXAMPLE

All J_7-primes are odd.

CROSSREFS

A163782 through A163786 for J_2- through J_6-primes. A163788 through A163800 for J_8- through J_20-primes.

Sequence in context: A166480 A164096 A298785 * A166863 A163704 A131898

Adjacent sequences:  A163784 A163785 A163786 * A163788 A163789 A163790

KEYWORD

nonn,more

AUTHOR

Peter R. J. Asveld, Aug 05 2009

STATUS

approved

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Last modified April 6 15:41 EDT 2020. Contains 333276 sequences. (Running on oeis4.)