640815 has 32 divisors (see below), whose sum is σ = 1244160. Its totient is φ = 274944.

The previous prime is 640793. The next prime is 640837. The reversal of 640815 is 518046.

It is an interprime number because it is at equal distance from previous prime (640793) and next prime (640837).

It is not a de Polignac number, because 640815 - 2⁷ = 640687 is a prime.

640815 is a lucky number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1606 + ... + 1964.

It is an arithmetic number, because the mean of its divisors is an integer number (38880).

2⁶⁴⁰⁸¹⁵ is an apocalyptic number.

640815 is a deficient number, since it is larger than the sum of its proper divisors (603345).

640815 is a wasteful number, since it uses less digits than its factorization.

640815 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 391.

The product of its (nonzero) digits is 960, while the sum is 24.

The square root of 640815 is about 800.5092129389. The cubic root of 640815 is about 86.2139525903.

The spelling of 640815 in words is "six hundred forty thousand, eight hundred fifteen".