Tài liệu tham khảo WikiPedia: 142857 http://findarticles.com/p/articles/mi_hb4870/is_20... http://www.daviddarling.info/encyclopedia/C/cyclic... //www.jstor.org/stable/3026586 http://planetmath.org/encyclopedia/CyclicNumber.ht... https://web.archive.org/web/20070714114415/http://... https://web.archive.org/web/20070929122525/http://... https://web.archive.org/web/20071224191059/http://... https://oeis.org/A006886
