This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A163800 #28 Apr 25 2025 03:07:35 %S A163800 2,5,30,54,81,109,149,186,513,1089,8158,8533,17178,34478,913274,976402 %N A163800 a(n) is the n-th J_20-prime (Josephus_20 prime). %C A163800 Place the numbers 1..N (N>=2) on a circle and cyclicly mark the 20th unmarked number until all N numbers are marked. The order in which the N numbers are marked defines a permutation; N is a J_20-prime if this permutation consists of a single cycle of length N. %C A163800 There are 16 J_20-primes in the interval 2..1000000 only. No formula is known; the J_20-primes were found by exhaustive search. %D A163800 R. L. Graham, D. E. Knuth & O. Patashnik, Concrete Mathematics (1989), Addison-Wesley, Reading, MA. Sections 1.3 & 3.3. %H A163800 Jean-Paul Allouche, Manon Stipulanti, and Jia-Yan Yao, <a href="https://arxiv.org/abs/2504.17564">Doubling modulo odd integers, generalizations, and unexpected occurrences</a>, arXiv:2504.17564 [math.NT], 2025. %H A163800 P. R. J. Asveld, <a href="http://dx.doi.org/10.1016/j.dam.2011.07.019">Permuting operations on strings and their relation to prime numbers</a>, Discrete Applied Mathematics 159 (2011) 1915-1932. %H A163800 P. R. J. Asveld, <a href="https://citeseerx.ist.psu.edu/pdf/9d8542763057ef03a22b57f87085d69497ddaf46">Permuting Operations on Strings-Their Permutations and Their Primes</a>, Twente University of Technology, 2014. <a href="http://doc.utwente.nl/67513">University link</a>. %H A163800 <a href="/index/J#Josephus">Index entries for sequences related to the Josephus Problem</a> %e A163800 2 is a J_20-prime (trivial). %Y A163800 See A163782 through A163799 for J_2- through J_19-primes. %K A163800 nonn,more %O A163800 1,1 %A A163800 _Peter R. J. Asveld_, Aug 04 2009, Aug 12 2009