640747 has 4 divisors (see below), whose sum is σ = 678456. Its totient is φ = 603040.

The previous prime is 640741. The next prime is 640771. The reversal of 640747 is 747046.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 640747 - 2¹¹ = 638699 is a prime.

It is a Duffinian number.

640747 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (640741) 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, 18829 + ... + 18862.

It is an arithmetic number, because the mean of its divisors is an integer number (169614).

2⁶⁴⁰⁷⁴⁷ is an apocalyptic number.

640747 is a deficient number, since it is larger than the sum of its proper divisors (37709).

640747 is a wasteful number, since it uses less digits than its factorization.

640747 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 37708.

The product of its (nonzero) digits is 4704, while the sum is 28.

The square root of 640747 is about 800.4667388468. The cubic root of 640747 is about 86.2109029550.

The spelling of 640747 in words is "six hundred forty thousand, seven hundred forty-seven".