Step inside the mysteries of the Number 9. Pen, paper and a digital calculator it’s all you need to embark in this journey. Enjoy!
Credits:
GARDNER, Martin, “Digital Roots”, Mathematics, Magic and Mystery, Dover Publications Inc, 1956, New York, p. 164-165.
BENJAMIN, Arthur T., THE SECRETS OF MENTAL MATH, The Great Courses Plus, The Teaching Company, United States Of America, 2011.
