640781813 has 4 divisors (see below), whose sum is σ = 732322080. Its totient is φ = 549241548.

The previous prime is 640781789. The next prime is 640781837. The reversal of 640781813 is 318187046.

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 (640781789) and next prime (640781837).

It is a cyclic number.

It is not a de Polignac number, because 640781813 - 2²² = 636587509 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640781893) 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, 45770123 + ... + 45770136.

It is an arithmetic number, because the mean of its divisors is an integer number (183080520).

Almost surely, 2^640781813 is an apocalyptic number.

It is an amenable number.

640781813 is a deficient number, since it is larger than the sum of its proper divisors (91540267).

640781813 is an equidigital number, since it uses as much as digits as its factorization.

640781813 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 91540266.

The product of its (nonzero) digits is 32256, while the sum is 38.

The square root of 640781813 is about 25313.6685014243. The cubic root of 640781813 is about 862.1246426064.

The spelling of 640781813 in words is "six hundred forty million, seven hundred eighty-one thousand, eight hundred thirteen".