640961628 has 12 divisors (see below), whose sum is σ = 1495577160. Its totient is φ = 213653872.

The previous prime is 640961627. The next prime is 640961639. The reversal of 640961628 is 826169046.

It is a tau number, because it is divible by the number of its divisors (12).

It is a Smith number, since the sum of its digits (42) coincides with the sum of the digits of its prime factors.

It is a self number, because there is not a number n which added to its sum of digits gives 640961628.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640961621) 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 3 ways as a sum of consecutive naturals, for example, 26706723 + ... + 26706746.

It is an arithmetic number, because the mean of its divisors is an integer number (124631430).

Almost surely, 2^640961628 is an apocalyptic number.

It is an amenable number.

640961628 is an abundant number, since it is smaller than the sum of its proper divisors (854615532).

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

640961628 is a wasteful number, since it uses less digits than its factorization.

640961628 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53413476 (or 53413474 counting only the distinct ones).

The product of its (nonzero) digits is 124416, while the sum is 42.

The square root of 640961628 is about 25317.2199895644. The cubic root of 640961628 is about 862.2052776687.

The spelling of 640961628 in words is "six hundred forty million, nine hundred sixty-one thousand, six hundred twenty-eight".