2000, the round-number year 2000 was widely celebrated. Technically, the 3rd millennium did not begin until January 1, 2001, a year later. Round number bias Round number bias is the psychological tendency to prefer round numbers over others, which is passed onto a person through socialization. Round numbers are also easier for a person to remember, process, and perform mathematical operations on. Round number bias has been observed in American and Chinese stock markets and stock prices in general, in retail and grocery, where prices are often just slightly less than a rounded number (ex. $9.99 or $9.95), in investments, including crowdfunding, in the real estate market through mortgages, and number milestones. Round numbers are often used when estimating the time taken to complete a task. Mathematics A round number is mathematically defined as an integer which is the product of a considerable number of comparatively small factors as compared to its neighboring numbers, such as 24 = 2 × 2 × 2 × 3 (4 factors, as opposed to 3 factors for 27; 2 factors for 21, 22, 25, and 26; and 1 factor for 23). See also Rounding Rounding fraud Significant figures Smooth number Unix billennium References Numbers