640899856 has 15 divisors (see below), whose sum is σ = 1241939701. Its totient is φ = 320399296.

The previous prime is 640899851. The next prime is 640899869. The reversal of 640899856 is 658998046.

The square root of 640899856 is 25316.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 489117456 + 151782400 = 22116^2 + 12320^2 .

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 640899797 and 640899806.

It is not an unprimeable number, because it can be changed into a prime (640899851) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 98100 + ... + 104428.

Almost surely, 2^640899856 is an apocalyptic number.

640899856 is the 25316-th square number.

It is an amenable number.

640899856 is a deficient number, since it is larger than the sum of its proper divisors (601039845).

640899856 is an frugal number, since it uses more digits than its factorization.

640899856 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12666 (or 6331 counting only the distinct ones).

The product of its (nonzero) digits is 3732480, while the sum is 55.

The cubic root of 640899856 is about 862.1775787378.

The spelling of 640899856 in words is "six hundred forty million, eight hundred ninety-nine thousand, eight hundred fifty-six".