71

71 is a natural number that follows 70 and precedes 72. In mathematics it is a prime number, specifically the 20th prime. It is also a Gaussian prime, since 71 is congruent to 3 modulo 4. In different numeral systems, 71 is written as 1000111 in binary and 47 in hexadecimal; in Roman numerals it is LXXI. In the ASCII character set, decimal 71 corresponds to the uppercase letter G.

In the periodic table, element 71 is lutetium (Lu), a silvery‑white lanthanide metal. Lutetium lies at the end of the lanthanide series and occurs only in trace amounts in minerals. It was discovered in 1907 independently by Georges Urbain and by Carl Auer von Welsbach, and it is named after Lutetia, the ancient name for Paris. Lutetium has niche applications in catalysts, certain types of lighting phosphors, and some high‑end electronics.

In astronomy, Messier 71 (M71) is a globular star cluster located in the constellation Sagitta. It is a member of the Milky Way’s halo and is relatively faint compared with many other globular clusters, making it more challenging to observe without a telescope.

Calendar and culture usage include the fact that the 71st day of the year is March 12 in common years and March 11 in leap years. The number 71 also appears in various designations and identifiers, such as highway numbers like Interstate 71 or U.S. Route 71.