643555656 has 24 divisors (see below), whose sum is σ = 1742963430. Its totient is φ = 214518528.

The previous prime is 643555637. The next prime is 643555727. The reversal of 643555656 is 656555346.

643555656 is a `hidden beast` number, since 6 + 43 + 5 + 556 + 56 = 666.

It can be written as a sum of positive squares in only one way, i.e., 642622500 + 933156 = 25350^2 + 966^2 .

It is a tau number, because it is divible by the number of its divisors (24).

It is a hoax number, since the sum of its digits (45) coincides with the sum of the digits of its distinct prime factors.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 4469065 + ... + 4469208.

Almost surely, 2^643555656 is an apocalyptic number.

It is an amenable number.

643555656 is an abundant number, since it is smaller than the sum of its proper divisors (1099407774).

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

643555656 is a wasteful number, since it uses less digits than its factorization.

643555656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8938285 (or 8938278 counting only the distinct ones).

The product of its digits is 1620000, while the sum is 45.

The square root of 643555656 is about 25368.3987669699. The cubic root of 643555656 is about 863.3668522372.

The spelling of 643555656 in words is "six hundred forty-three million, five hundred fifty-five thousand, six hundred fifty-six".