Fatto generale: 81 is the number of stanzas or chapters in the Tao te Ching (in the most common arrangements).
Fatto matematico: 81 is the square of the sum of its digits.
Trivia: 81 is the number of stanzas or chapters in the Tao te Ching (in the most common arrangements).
Data storica: March 21st is the day in 1801 that the Battle of Alexandria is fought between British and French forces near the ruins of Nicopolis in Egypt.