6404639856 has 80 divisors (see below), whose sum is σ = 16839303168. Its totient is φ = 2097043200.

The previous prime is 6404639849. The next prime is 6404639863. The reversal of 6404639856 is 6589364046.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (6404639849) and next prime (6404639863).

It is a Smith number, since the sum of its digits (51) coincides with the sum of the digits of its prime factors.

It is a junction number, because it is equal to n+sod(n) for n = 6404639799 and 6404639808.

It is a congruent number.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 4306345 + ... + 4307831.

Almost surely, 2^6404639856 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 6404639856, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (8419651584).

6404639856 is an abundant number, since it is smaller than the sum of its proper divisors (10434663312).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

6404639856 is a wasteful number, since it uses less digits than its factorization.

6404639856 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3030 (or 3024 counting only the distinct ones).

The product of its (nonzero) digits is 3732480, while the sum is 51.

The square root of 6404639856 is about 80028.9938459806. The cubic root of 6404639856 is about 1857.0840980586.

The spelling of 6404639856 in words is "six billion, four hundred four million, six hundred thirty-nine thousand, eight hundred fifty-six".