84

84 is the natural number that follows 83 and precedes 85. It is even and composite, with prime factorization 2^2 * 3 * 7. It has 12 divisors: 1, 2, 3, 4, 6, 7, 12, 14, 21, 28, 42, and 84. The sum of its proper divisors is 140, making 84 an abundant number with abundance 56. In various numeral bases, 84 is written as 1010100 in binary, 0x54 in hexadecimal, 124 in octal, and 10010 in base 3.

84 is also represented in Roman numerals as LXXXIV.

84 is the atomic number of polonium (Po), a radioactive element discovered by Marie and Pierre Curie in 1898 and named after Poland. Polonium has several isotopes, all radioactive; it has been used as a heat source in space equipment and historically in antistatic devices, but remains highly toxic and hazardous.

On calendars, day 84 falls on March 25 in common years and March 24 in leap years.