640921906 has 8 divisors (see below), whose sum is σ = 961728624. Its totient is φ = 320345700.

The previous prime is 640921903. The next prime is 640921991. The reversal of 640921906 is 609129046.

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

It is not an unprimeable number, because it can be changed into a prime (640921901) 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, 50500 + ... + 61903.

It is an arithmetic number, because the mean of its divisors is an integer number (120216078).

Almost surely, 2^640921906 is an apocalyptic number.

640921906 is a deficient number, since it is larger than the sum of its proper divisors (320806718).

640921906 is a wasteful number, since it uses less digits than its factorization.

640921906 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 115256.

The product of its (nonzero) digits is 23328, while the sum is 37.

The square root of 640921906 is about 25316.4354915932. The cubic root of 640921906 is about 862.1874662927.

The spelling of 640921906 in words is "six hundred forty million, nine hundred twenty-one thousand, nine hundred six".