640805 has 16 divisors (see below), whose sum is σ = 857088. Its totient is φ = 456000.

The previous prime is 640793. The next prime is 640837. The reversal of 640805 is 508046.

640805 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 640805 - 2⁶ = 640741 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3260 + ... + 3450.

It is an arithmetic number, because the mean of its divisors is an integer number (53568).

2⁶⁴⁰⁸⁰⁵ is an apocalyptic number.

It is an amenable number.

640805 is a deficient number, since it is larger than the sum of its proper divisors (216283).

640805 is a wasteful number, since it uses less digits than its factorization.

640805 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 268.

The product of its (nonzero) digits is 960, while the sum is 23.

The square root of 640805 is about 800.5029668902. The cubic root of 640805 is about 86.2135041280.

It can be divided in two parts, 64080 and 5, that multiplied together give a triangular number (320400 = T₈₀₀).

The spelling of 640805 in words is "six hundred forty thousand, eight hundred five".