640605218 has 18 divisors (see below), whose sum is σ = 1056854043. Its totient is φ = 291005220.

The previous prime is 640605211. The next prime is 640605221. The reversal of 640605218 is 812506046.

It can be written as a sum of positive squares in only one way, i.e., 320302609 + 320302609 = 17897^2 + 17897^2 .

It is an ABA number since it can be written as A⋅B^A, here for A=2, B=17897.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (640605211) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 392921 + ... + 394547.

Almost surely, 2^640605218 is an apocalyptic number.

640605218 is a deficient number, since it is larger than the sum of its proper divisors (416248825).

640605218 is an equidigital number, since it uses as much as digits as its factorization.

640605218 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3278 (or 1640 counting only the distinct ones).

The product of its (nonzero) digits is 11520, while the sum is 32.

The square root of 640605218 is about 25310.1801257913. The cubic root of 640605218 is about 862.0454368163.

Multiplying 640605218 by its sum of digits (32), we get a square (20499366976 = 143176²).

The spelling of 640605218 in words is "six hundred forty million, six hundred five thousand, two hundred eighteen".