Tài liệu tham khảo

WikiPedia: Số http://www.britannica.com/EBchecked/topic/422286 http://www.oed.com/view/Entry/129082 http://www.oed.com/view/Entry/129111 http://www.math.buffalo.edu/mad/Ancient-Africa/mad... http://sunsite.utk.edu/math_archives/.http/hyperma... //dx.doi.org/10.1017%2FS0003598X00092541 //www.worldcat.org/issn/0003-598X https://books.google.com/books?id=dOxl71w-jHEC&pg=... https://books.google.com/books?id=f6HlhlBuQUgC&pg=... https://www.scientificamerican.com/article/history...