640555209 has 40 divisors (see below), whose sum is σ = 1095946368. Its totient is φ = 365238720.

The previous prime is 640555187. The next prime is 640555241. The reversal of 640555209 is 902555046.

640555209 is a `hidden beast` number, since 640 + 5 + 5 + 5 + 2 + 0 + 9 = 666.

It is not a de Polignac number, because 640555209 - 2⁷ = 640555081 is a prime.

It is not an unprimeable number, because it can be changed into a prime (640555009) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 348924 + ... + 350754.

Almost surely, 2^640555209 is an apocalyptic number.

It is an amenable number.

640555209 is a deficient number, since it is larger than the sum of its proper divisors (455391159).

640555209 is a wasteful number, since it uses less digits than its factorization.

640555209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2467 (or 2458 counting only the distinct ones).

The product of its (nonzero) digits is 54000, while the sum is 36.

The square root of 640555209 is about 25309.1921838687. The cubic root of 640555209 is about 862.0230043046.

The spelling of 640555209 in words is "six hundred forty million, five hundred fifty-five thousand, two hundred nine".