640399809 has 32 divisors (see below), whose sum is σ = 1039322880. Its totient is φ = 342392832.

The previous prime is 640399789. The next prime is 640399819. The reversal of 640399809 is 908993046.

It is a happy number.

640399809 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 640399809 - 2⁹ = 640399297 is a prime.

It is a super-2 number, since 2×640399809² = 820223830734472962, which contains 22 as substring.

It is a Smith number, since the sum of its digits (48) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is not an unprimeable number, because it can be changed into a prime (640399819) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 56577 + ... + 66945.

It is an arithmetic number, because the mean of its divisors is an integer number (32478840).

Almost surely, 2^640399809 is an apocalyptic number.

It is an amenable number.

640399809 is a deficient number, since it is larger than the sum of its proper divisors (398923071).

640399809 is a wasteful number, since it uses less digits than its factorization.

640399809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10569.

The product of its (nonzero) digits is 419904, while the sum is 48.

The square root of 640399809 is about 25306.1219668285. The cubic root of 640399809 is about 861.9532891537.

The spelling of 640399809 in words is "six hundred forty million, three hundred ninety-nine thousand, eight hundred nine".