87

87 is a natural number that comes after 86 and before 88. In mathematics, it is an odd composite number and the product of two primes, 3 and 29.

Its prime factorization: 87 = 3 × 29. It is a semiprime. It is congruent to 3 mod 4. Its proper divisors are 1, 3, and 29. Representations: in Roman numerals LXXXVII; in binary 1010111; in base-3 10020; in hexadecimal 57.

In science, 87 denotes the atomic number of francium, a highly radioactive alkali metal. Francium is extremely rare in the Earth's crust and typically produced from decay of actinium. It has no stable isotopes and is highly reactive.

In astronomy, Messier 87 (M87) is a giant elliptical galaxy in the Virgo Cluster, notable for hosting a strong supermassive black hole whose image was captured by the Event Horizon Telescope in 2019.

In culture and notation, 87 is commonly used to denote the year 1987 and, in ASCII, the code 87 corresponds to the uppercase letter W.