640393657 has 2 divisors, whose sum is σ = 640393658. Its totient is φ = 640393656.

The previous prime is 640393603. The next prime is 640393667. The reversal of 640393657 is 756393046.

640393657 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 623550841 + 16842816 = 24971^2 + 4104^2 .

It is a cyclic number.

It is not a de Polignac number, because 640393657 - 2⁷ = 640393529 is a prime.

It is not a weakly prime, because it can be changed into another prime (640393667) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320196828 + 320196829.

It is an arithmetic number, because the mean of its divisors is an integer number (320196829).

Almost surely, 2^640393657 is an apocalyptic number.

It is an amenable number.

640393657 is a deficient number, since it is larger than the sum of its proper divisors (1).

640393657 is an equidigital number, since it uses as much as digits as its factorization.

640393657 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 408240, while the sum is 43.

The square root of 640393657 is about 25306.0004149214. Note that the first 3 decimals coincide. The cubic root of 640393657 is about 861.9505290271.

The spelling of 640393657 in words is "six hundred forty million, three hundred ninety-three thousand, six hundred fifty-seven".