640991931 has 8 divisors (see below), whose sum is σ = 858421824. Its totient is φ = 425445000.

The previous prime is 640991917. The next prime is 640991941. The reversal of 640991931 is 139199046.

640991931 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 640991931 - 2⁷ = 640991803 is a prime.

It is a super-2 number, since 2×640991931² = 821741311214217522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (640991941) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 469945 + ... + 471306.

It is an arithmetic number, because the mean of its divisors is an integer number (107302728).

Almost surely, 2^640991931 is an apocalyptic number.

640991931 is a deficient number, since it is larger than the sum of its proper divisors (217429893).

640991931 is a wasteful number, since it uses less digits than its factorization.

640991931 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 941481.

The product of its (nonzero) digits is 52488, while the sum is 42.

The square root of 640991931 is about 25317.8184486737. The cubic root of 640991931 is about 862.2188650628.

The spelling of 640991931 in words is "six hundred forty million, nine hundred ninety-one thousand, nine hundred thirty-one".