Year 0 does not exist in the AD calendar. The year before AD 1 is 1 BC. Because of this, the 21st century began not in 2000 but in 2001.

Across diverse numerical data—bank balances, populations, prices—the first digit is most often 1 and least often 9. This is known as Benford's law, and accounting records that deviate from this pattern may indicate fraud.