640709 has 4 divisors (see below), whose sum is σ = 643104. Its totient is φ = 638316.

The previous prime is 640691. The next prime is 640727. The reversal of 640709 is 907046.

640709 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is an interprime number because it is at equal distance from previous prime (640691) and next prime (640727).

It is a cyclic number.

It is not a de Polignac number, because 640709 - 2¹² = 636613 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 640709.

It is not an unprimeable number, because it can be changed into a prime (640009) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 737 + ... + 1350.

It is an arithmetic number, because the mean of its divisors is an integer number (160776).

2⁶⁴⁰⁷⁰⁹ is an apocalyptic number.

It is an amenable number.

640709 is a deficient number, since it is larger than the sum of its proper divisors (2395).

640709 is a wasteful number, since it uses less digits than its factorization.

640709 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2394.

The product of its (nonzero) digits is 1512, while the sum is 26.

The square root of 640709 is about 800.4430023431. The cubic root of 640709 is about 86.2091986530.

The spelling of 640709 in words is "six hundred forty thousand, seven hundred nine".