Tatu ni namba ambayo inafuata mbili na kutangulia nne. Kwa kawaida inaandikwa 3 lakini III kwa namba za Kiroma na ٣ kwa zile za Kiarabu. 3 ni namba tasa. Wells, D. The Penguin Dictionary of Curious and Interesting Numbers London: Penguin Group (1987): 70–71 Wikimedia Commons ina media kuhusu: Tatu Tricyclopedic Book of Threes by Michael Eck Threes in Human Anatomy by Dr. John A. McNulty Grime, James. 3 is everywhere. Numberphile. Brady Haran. Jalada kutoka ya awali juu ya 2013-05-14. Iliwekwa mnamo 2015-02-24. The Number 3 The Positive Integer 3 Prime curiosities: 3