640799991 has 48 divisors (see below), whose sum is σ = 1043762720. Its totient is φ = 390510720.

The previous prime is 640799969. The next prime is 640800031. The reversal of 640799991 is 199997046.

It is not a de Polignac number, because 640799991 - 2¹¹ = 640797943 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640719991) 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 47 ways as a sum of consecutive naturals, for example, 343401 + ... + 345261.

Almost surely, 2^640799991 is an apocalyptic number.

640799991 is a deficient number, since it is larger than the sum of its proper divisors (402962729).

640799991 is a wasteful number, since it uses less digits than its factorization.

640799991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1998 (or 1986 counting only the distinct ones).

The product of its (nonzero) digits is 1102248, while the sum is 54.

The square root of 640799991 is about 25314.0275539077. The cubic root of 640799991 is about 862.1327949152.

The spelling of 640799991 in words is "six hundred forty million, seven hundred ninety-nine thousand, nine hundred ninety-one".