640799 has 4 divisors (see below), whose sum is σ = 651720. Its totient is φ = 629880.

The previous prime is 640793. The next prime is 640837. The reversal of 640799 is 997046.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 997046 = 2 ⋅498523.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640799 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640793) 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, 5372 + ... + 5489.

It is an arithmetic number, because the mean of its divisors is an integer number (162930).

2⁶⁴⁰⁷⁹⁹ is an apocalyptic number.

640799 is a deficient number, since it is larger than the sum of its proper divisors (10921).

640799 is a wasteful number, since it uses less digits than its factorization.

640799 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10920.

The product of its (nonzero) digits is 13608, while the sum is 35.

The square root of 640799 is about 800.4992192376. The cubic root of 640799 is about 86.2132350484.

The spelling of 640799 in words is "six hundred forty thousand, seven hundred ninety-nine".