640805813 has 4 divisors (see below), whose sum is σ = 641292960. Its totient is φ = 640318668.

The previous prime is 640805807. The next prime is 640805819. The reversal of 640805813 is 318508046.

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 (640805807) and next prime (640805819).

It is a cyclic number.

It is not a de Polignac number, because 640805813 - 2⁶ = 640805749 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 (640805819) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 241595 + ... + 244232.

It is an arithmetic number, because the mean of its divisors is an integer number (160323240).

Almost surely, 2^640805813 is an apocalyptic number.

It is an amenable number.

640805813 is a deficient number, since it is larger than the sum of its proper divisors (487147).

640805813 is a wasteful number, since it uses less digits than its factorization.

640805813 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 487146.

The product of its (nonzero) digits is 23040, while the sum is 35.

The square root of 640805813 is about 25314.1425491759. The cubic root of 640805813 is about 862.1354058817.

The spelling of 640805813 in words is "six hundred forty million, eight hundred five thousand, eight hundred thirteen".