6440681856 has 128 divisors (see below), whose sum is σ = 19623951360. Its totient is φ = 1833431040.

The previous prime is 6440681839. The next prime is 6440681867. The reversal of 6440681856 is 6581860446.

It is a tau number, because it is divible by the number of its divisors (128).

It is a Harshad number since it is a multiple of its sum of digits (48).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 751065 + ... + 759591.

It is an arithmetic number, because the mean of its divisors is an integer number (153312120).

Almost surely, 2^6440681856 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 6440681856, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (9811975680).

6440681856 is an abundant number, since it is smaller than the sum of its proper divisors (13183269504).

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

6440681856 is a wasteful number, since it uses less digits than its factorization.

6440681856 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8832 (or 8820 counting only the distinct ones).

The product of its (nonzero) digits is 1105920, while the sum is 48.

The square root of 6440681856 is about 80253.8588231121. The cubic root of 6440681856 is about 1860.5611533819.

The spelling of 6440681856 in words is "six billion, four hundred forty million, six hundred eighty-one thousand, eight hundred fifty-six".