640821309 has 8 divisors (see below), whose sum is σ = 855927072. Its totient is φ = 426464880.

The previous prime is 640821301. The next prime is 640821317. The reversal of 640821309 is 903128046.

It is an interprime number because it is at equal distance from previous prime (640821301) and next prime (640821317).

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

It is not a de Polignac number, because 640821309 - 2³ = 640821301 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 640821309.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640821301) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 185334 + ... + 188759.

It is an arithmetic number, because the mean of its divisors is an integer number (106990884).

Almost surely, 2^640821309 is an apocalyptic number.

It is an amenable number.

640821309 is a deficient number, since it is larger than the sum of its proper divisors (215105763).

640821309 is a wasteful number, since it uses less digits than its factorization.

640821309 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 374667.

The product of its (nonzero) digits is 10368, while the sum is 33.

The square root of 640821309 is about 25314.4486212914. The cubic root of 640821309 is about 862.1423552270.

The spelling of 640821309 in words is "six hundred forty million, eight hundred twenty-one thousand, three hundred nine".