101

101 is a natural number that follows 100 and precedes 102. In base-10 notation, it is a palindromic, odd three-digit prime and the 26th prime number.

In other numeral systems, 101 has distinct representations: in binary it is 1100101, and in hexadecimal it is 0x65. In Roman numerals it is written as CI. As a mathematical fact, 101 is a prime that can be expressed as the sum of two squares: 101 = 10^2 + 1^2.

101 also appears in science and technology. It is the atomic number of the synthetic element mendelevium (Md), part of the actinide series. In computing, HTTP status code 101 indicates a switch of protocols as part of establishing a different communication method. In ASCII, the decimal value 101 corresponds to the lowercase letter e.

In culture and daily use, 101 is widely used to signify introductory material, as in courses labeled 101 (for example, Math 101 or Biology 101). It has appeared in popular titles such as the film 101 Dalmatians. The number also features in transportation geography, notably U.S. Route 101, a major north–south highway along much of the West Coast of the United States.

Overall, 101 is a prime number with multiple representations, a small set of mathematical properties, and a place in science, technology, education, and culture.