640709906 has 16 divisors (see below), whose sum is σ = 1071156960. Its totient is φ = 285641280.

The previous prime is 640709903. The next prime is 640709917. The reversal of 640709906 is 609907046.

It is not an unprimeable number, because it can be changed into a prime (640709903) 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, 495260 + ... + 496551.

It is an arithmetic number, because the mean of its divisors is an integer number (66947310).

Almost surely, 2^640709906 is an apocalyptic number.

640709906 is a deficient number, since it is larger than the sum of its proper divisors (430447054).

640709906 is a wasteful number, since it uses less digits than its factorization.

640709906 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 991849.

The product of its (nonzero) digits is 81648, while the sum is 41.

The square root of 640709906 is about 25312.2481419569. The cubic root of 640709906 is about 862.0923928794.

The spelling of 640709906 in words is "six hundred forty million, seven hundred nine thousand, nine hundred six".