640646717 has 8 divisors (see below), whose sum is σ = 678814200. Its totient is φ = 602532864.

The previous prime is 640646711. The next prime is 640646729. The reversal of 640646717 is 717646046.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 116877721 + 523768996 = 10811^2 + 22886^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 640646717 - 2¹⁰ = 640645693 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640646711) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 12659 + ... + 37967.

It is an arithmetic number, because the mean of its divisors is an integer number (84851775).

Almost surely, 2^640646717 is an apocalyptic number.

It is an amenable number.

640646717 is a deficient number, since it is larger than the sum of its proper divisors (38167483).

640646717 is a wasteful number, since it uses less digits than its factorization.

640646717 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26815.

The product of its (nonzero) digits is 169344, while the sum is 41.

The square root of 640646717 is about 25310.9999209830. Note that the first 4 decimals coincide. The cubic root of 640646717 is about 862.0640511152.

The spelling of 640646717 in words is "six hundred forty million, six hundred forty-six thousand, seven hundred seventeen".