640779 has 8 divisors (see below), whose sum is σ = 860160. Its totient is φ = 424296.

The previous prime is 640777. The next prime is 640793. The reversal of 640779 is 977046.

640779 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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

It is not a de Polignac number, because 640779 - 2¹ = 640777 is a prime.

640779 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (640771) 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, 139 + ... + 1140.

It is an arithmetic number, because the mean of its divisors is an integer number (107520).

2⁶⁴⁰⁷⁷⁹ is an apocalyptic number.

640779 is a deficient number, since it is larger than the sum of its proper divisors (219381).

640779 is a wasteful number, since it uses less digits than its factorization.

640779 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1449.

The product of its (nonzero) digits is 10584, while the sum is 33.

The square root of 640779 is about 800.4867269356. The cubic root of 640779 is about 86.2123381043.

The spelling of 640779 in words is "six hundred forty thousand, seven hundred seventy-nine".