640690 has 16 divisors (see below), whose sum is σ = 1169280. Its totient is φ = 252720.

The previous prime is 640687. The next prime is 640691. The reversal of 640690 is 96046.

640690 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a super-2 number, since 2×640690² = 820967352200, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (640691) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 385 + ... + 1195.

It is an arithmetic number, because the mean of its divisors is an integer number (73080).

2⁶⁴⁰⁶⁹⁰ is an apocalyptic number.

640690 is a deficient number, since it is larger than the sum of its proper divisors (528590).

640690 is a wasteful number, since it uses less digits than its factorization.

640690 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 897.

The product of its (nonzero) digits is 1296, while the sum is 25.

The square root of 640690 is about 800.4311338273. The cubic root of 640690 is about 86.2083464768.

Subtracting from 640690 its reverse (96046), we obtain a square (544644 = 738²).

The spelling of 640690 in words is "six hundred forty thousand, six hundred ninety".