640685 has 8 divisors (see below), whose sum is σ = 777336. Its totient is φ = 506880.

The previous prime is 640669. The next prime is 640687. The reversal of 640685 is 586046.

It can be written as a sum of positive squares in 4 ways, for example, as 175561 + 465124 = 419^2 + 682^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 640685 - 2⁴ = 640669 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640687) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 176 + ... + 1145.

It is an arithmetic number, because the mean of its divisors is an integer number (97167).

2⁶⁴⁰⁶⁸⁵ is an apocalyptic number.

It is an amenable number.

640685 is a deficient number, since it is larger than the sum of its proper divisors (136651).

640685 is a wasteful number, since it uses less digits than its factorization.

640685 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1423.

The product of its (nonzero) digits is 5760, while the sum is 29.

The square root of 640685 is about 800.4280105044. The cubic root of 640685 is about 86.2081222171.

The spelling of 640685 in words is "six hundred forty thousand, six hundred eighty-five".