639581 has 4 divisors (see below), whose sum is σ = 643452. Its totient is φ = 635712.

The previous prime is 639577. The next prime is 639589. The reversal of 639581 is 185936.

639581 = 565² + 566².

639581 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 319225 + 320356 = 565^2 + 566^2 .

It is a cyclic number.

It is not a de Polignac number, because 639581 - 2² = 639577 is a prime.

It is a super-2 number, since 2×639581² = 818127711122, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 639581.

It is not an unprimeable number, because it can be changed into a prime (639589) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1676 + ... + 2021.

It is an arithmetic number, because the mean of its divisors is an integer number (160863).

2⁶³⁹⁵⁸¹ is an apocalyptic number.

639581 is the 566-th centered square number.

It is an amenable number.

639581 is a deficient number, since it is larger than the sum of its proper divisors (3871).

639581 is a wasteful number, since it uses less digits than its factorization.

639581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3870.

The product of its digits is 6480, while the sum is 32.

The square root of 639581 is about 799.7380821244. The cubic root of 639581 is about 86.1585770762.

The spelling of 639581 in words is "six hundred thirty-nine thousand, five hundred eighty-one".