640091 has 8 divisors (see below), whose sum is σ = 686400. Its totient is φ = 595080.

The previous prime is 640069. The next prime is 640099. The reversal of 640091 is 190046.

640091 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 640091 - 2⁶ = 640027 is a prime.

It is a Duffinian number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 640091.

It is not an unprimeable number, because it can be changed into a prime (640099) 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, 836 + ... + 1406.

It is an arithmetic number, because the mean of its divisors is an integer number (85800).

2⁶⁴⁰⁰⁹¹ is an apocalyptic number.

640091 is a deficient number, since it is larger than the sum of its proper divisors (46309).

640091 is a wasteful number, since it uses less digits than its factorization.

640091 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 649.

The product of its (nonzero) digits is 216, while the sum is 20.

The square root of 640091 is about 800.0568729784. The cubic root of 640091 is about 86.1814718568.

The spelling of 640091 in words is "six hundred forty thousand, ninety-one".