640040656 has 20 divisors (see below), whose sum is σ = 1242120772. Its totient is φ = 319493376.

The previous prime is 640040587. The next prime is 640040657. The reversal of 640040656 is 656040046.

It can be written as a sum of positive squares in 2 ways, for example, as 29160000 + 610880656 = 5400^2 + 24716^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640040657) 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, 22821 + ... + 42436.

Almost surely, 2^640040656 is an apocalyptic number.

It is an amenable number.

640040656 is a deficient number, since it is larger than the sum of its proper divisors (602080116).

640040656 is a wasteful number, since it uses less digits than its factorization.

640040656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 65878 (or 65872 counting only the distinct ones).

The product of its (nonzero) digits is 17280, while the sum is 31.

The square root of 640040656 is about 25299.0248033398. The cubic root of 640040656 is about 861.7921236882.

The spelling of 640040656 in words is "six hundred forty million, forty thousand, six hundred fifty-six".