640657817 has 8 divisors (see below), whose sum is σ = 659904960. Its totient is φ = 621608400.

The previous prime is 640657783. The next prime is 640657859. The reversal of 640657817 is 718756046.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640657817 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (640657877) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 42842 + ... + 55827.

It is an arithmetic number, because the mean of its divisors is an integer number (82488120).

Almost surely, 2^640657817 is an apocalyptic number.

It is an amenable number.

640657817 is a deficient number, since it is larger than the sum of its proper divisors (19247143).

640657817 is a wasteful number, since it uses less digits than its factorization.

640657817 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 98863.

The product of its (nonzero) digits is 282240, while the sum is 44.

The square root of 640657817 is about 25311.2191922870. The cubic root of 640657817 is about 862.0690298632.

The spelling of 640657817 in words is "six hundred forty million, six hundred fifty-seven thousand, eight hundred seventeen".