The Yoruba Vigesimal (Base 20) Numeral System

The vigesimal or base 20 numeral system is not new to the Yoruba. The Yoruba version was created by the philosopher/priest genius Ọ̀rúnmìla (The father of classical Yoruba philosophỳ) who lived around 500 BC and later deified by the Yoruba of that time. He was a contemporary of Socrates as they both lived during the same epoch. Just like Socrates, he did not write down anything but his disciples (named after the main Odu Ifa) codified his teachings into the Yoruba oral traditions.

Everything revolves around 20 (Ogún) primarily hence we have:
40 (Ogójì) - Ogún-meji (2 * 20)
60 (Ọgọ́ta) - Ogún-mẹ̀ta (3 * 20)
80 (Ọgọrin) - Ogún-mẹ̀rin (4 * 20)
100 (Ọgọrun) - Ogún-màrún (5 * 20)
120 (Ọgọfa) - Ogún-mefa (6 * 20)
140 (Ogoje) - Ogún-meje (7 * 20) etc

The highest number in this system is 20,000 which is called Ọ̀kẹ́ kan (one Ọ̀kẹ)́. Thereafter, larger numbers are reckoned as multiples of one Ọ̀kẹ́ e.g
100,000 is Ọ̀kẹ́ màrún (5 * 20,000),
1,000,000 is àádọ́ta ọ̀kẹ́ (50 * 20,000) and 2,000,000 is ọgọ́rùn ọ̀kẹ (100 * 20,000)

The uniqueness of the Yoruba version is that it augments mental arithmetic whereby addition and subtraction are performed mentally while counting e.g
15 - Marun- dín-lógún (20 minus 5)
16 - Mẹ́rin-dín-lógún (20 minus 4)
17 - Mẹ́ta-̀dín-lógún (20 minus 3)
18 - Méjì-dín-lógún (20 minus 2)
19 - Okan-din-logun (20 minus 1)
21 - Mọ́kàn-lé-lógún (20 plus 1)
22 - Mejì-lé-lógún (20 plus 2)
23 - Mẹta-lé-lógún (20 plus 3)
24 - Mẹ́rìn-lé-lógún (20 plus 4)