640909808 has 60 divisors (see below), whose sum is σ = 1575838872. Its totient is φ = 249701760.

The previous prime is 640909783. The next prime is 640909811. The reversal of 640909808 is 808909046.

It is a Harshad number since it is a multiple of its sum of digits (44).

It is a congruent number.

It is an unprimeable number.

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 11 ways as a sum of consecutive naturals, for example, 28535 + ... + 45782.

Almost surely, 2^640909808 is an apocalyptic number.

It is an amenable number.

640909808 is an abundant number, since it is smaller than the sum of its proper divisors (934929064).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

640909808 is a wasteful number, since it uses less digits than its factorization.

640909808 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 74350 (or 74337 counting only the distinct ones).

The product of its (nonzero) digits is 124416, while the sum is 44.

The square root of 640909808 is about 25316.1965547750. The cubic root of 640909808 is about 862.1820413938.

The spelling of 640909808 in words is "six hundred forty million, nine hundred nine thousand, eight hundred eight".