# 64 (number)

 ← 63 64 65 →
Cardinalsixty-four
Ordinal64th
(sixty-fourth)
Factorization26
Divisors1, 2, 4, 8, 16, 32, 64
Greek numeralΞΔ´
Roman numeralLXIV
Binary10000002
Ternary21013
Octal1008
Duodecimal5412

64 (sixty-four) is the natural number following 63 and preceding 65.

## In mathematics[]

Sixty-four is the square of 8, the cube of 4, and the sixth power of 2. It is the smallest number with exactly seven divisors. It is the lowest positive power of two that is adjacent to neither a Mersenne prime nor a Fermat prime. 64 is the sum of Euler's totient function for the first fourteen integers. It is also a dodecagonal number[1] and a centered triangular number.[2] 64 is also the first whole number (greater than 1) that is both a perfect square and a perfect cube.

Since it is possible to find sequences of 64 consecutive integers such that each inner member shares a factor with either the first or the last member, 64 is an Erdős–Woods number.[3]

In base 10, no integer added up to its own digits yields 64, hence it is a self number.[4]

64 is a superperfect number—a number such that σ(σ(n)) = 2n.[5]

64 is the index of Graham's number in the rapidly growing sequence 3↑↑↑↑3, 3 ↑3↑↑↑↑3 3,…

## In other fields[]

A chessboard has 64 squares

Sixty-four is: