What is 400?

400 is a composite number, an even number, and a Harshad number. It is the square of 20 and the sum of four consecutive prime numbers (97 + 101 + 103 + 107). In Roman numerals, 400 is represented as CD. It is a commonly used number in various contexts such as measurements (400 meters), time (400 seconds), and rankings (top 400 universities). In mathematics, 400 is also a perfect score on some standardized tests, such as the GRE. Additionally, 400 is the HTTP status code for a successful connection.