640991231 has 4 divisors (see below), whose sum is σ = 641151264. Its totient is φ = 640831200.

The previous prime is 640991191. The next prime is 640991249. The reversal of 640991231 is 132199046.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 640991231 - 2¹⁴ = 640974847 is a prime.

It is a super-2 number, since 2×640991231² = 821739516437790722, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 640991191 and 640991200.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640991251) 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, 73850 + ... + 82071.

It is an arithmetic number, because the mean of its divisors is an integer number (160287816).

Almost surely, 2^640991231 is an apocalyptic number.

640991231 is a deficient number, since it is larger than the sum of its proper divisors (160033).

640991231 is a wasteful number, since it uses less digits than its factorization.

640991231 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 160032.

The product of its (nonzero) digits is 11664, while the sum is 35.

The square root of 640991231 is about 25317.8046244140. The cubic root of 640991231 is about 862.2185511985.

The spelling of 640991231 in words is "six hundred forty million, nine hundred ninety-one thousand, two hundred thirty-one".