640685856 has 48 divisors (see below), whose sum is σ = 1686333600. Its totient is φ = 212986368.

The previous prime is 640685839. The next prime is 640685863. The reversal of 640685856 is 658586046.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (48).

It is a Harshad number since it is a multiple of its sum of digits (48).

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 27580 + ... + 45188.

It is an arithmetic number, because the mean of its divisors is an integer number (35131950).

Almost surely, 2^640685856 is an apocalyptic number.

It is an amenable number.

640685856 is an abundant number, since it is smaller than the sum of its proper divisors (1045647744).

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

640685856 is a wasteful number, since it uses less digits than its factorization.

640685856 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18001 (or 17993 counting only the distinct ones).

The product of its (nonzero) digits is 1382400, while the sum is 48.

The square root of 640685856 is about 25311.7730710434. The cubic root of 640685856 is about 862.0816061040.

The spelling of 640685856 in words is "six hundred forty million, six hundred eighty-five thousand, eight hundred fifty-six".