640664993 has 2 divisors, whose sum is σ = 640664994. Its totient is φ = 640664992.

The previous prime is 640664963. The next prime is 640665017. The reversal of 640664993 is 399466046.

640664993 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., 324252049 + 316412944 = 18007^2 + 17788^2 .

It is a cyclic number.

It is not a de Polignac number, because 640664993 - 2¹² = 640660897 is a prime.

It is not a weakly prime, because it can be changed into another prime (640664903) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320332496 + 320332497.

It is an arithmetic number, because the mean of its divisors is an integer number (320332497).

Almost surely, 2^640664993 is an apocalyptic number.

It is an amenable number.

640664993 is a deficient number, since it is larger than the sum of its proper divisors (1).

640664993 is an equidigital number, since it uses as much as digits as its factorization.

640664993 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 839808, while the sum is 47.

The square root of 640664993 is about 25311.3609472110. The cubic root of 640664993 is about 862.0722485259.

The spelling of 640664993 in words is "six hundred forty million, six hundred sixty-four thousand, nine hundred ninety-three".