84 (number)

84 (eighty-four) is the natural number following 83 and preceding 85.

84 is a semiperfect number,[1] being thrice a perfect number, and the sum of the sixth pair of twin primes

[2] It is the number of four-digit perfect powers in decimal.

[6] As no smaller number has more than 12 divisors, 84 is a largely composite number.

[7] The twenty-second unique prime in decimal, with notably different digits than its preceding (and known following) terms in the same sequence, contains a total of 84 digits.

[8] A hepteract is a seven-dimensional hypercube with 84 penteract 5-faces.

[9] 84 is the limit superior of the largest finite subgroup of the mapping class group of a genus

[citation needed] Under Hurwitz's automorphisms theorem, a smooth connected Riemann surface

whose order is classically bound to

(or unique factorization), preceding 60 (that is the composite index of 84),[11] and 48.