640684457 has 18 divisors (see below), whose sum is σ = 790027182. Its totient is φ = 516265344.

The previous prime is 640684453. The next prime is 640684459. The reversal of 640684457 is 754486046.

It can be written as a sum of positive squares in 3 ways, for example, as 404170816 + 236513641 = 20104^2 + 15379^2 .

It is not a de Polignac number, because 640684457 - 2² = 640684453 is a prime.

It is not an unprimeable number, because it can be changed into a prime (640684453) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 730103 + ... + 730979.

It is an arithmetic number, because the mean of its divisors is an integer number (43890399).

Almost surely, 2^640684457 is an apocalyptic number.

It is an amenable number.

640684457 is a deficient number, since it is larger than the sum of its proper divisors (149342725).

640684457 is an frugal number, since it uses more digits than its factorization.

640684457 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1785 (or 901 counting only the distinct ones).

The product of its (nonzero) digits is 645120, while the sum is 44.

The square root of 640684457 is about 25311.7454356668. The cubic root of 640684457 is about 862.0809786238.

The spelling of 640684457 in words is "six hundred forty million, six hundred eighty-four thousand, four hundred fifty-seven".