6643991808 has 108 divisors (see below), whose sum is σ = 19518064020. Its totient is φ = 2172837888.

The previous prime is 6643991803. The next prime is 6643991869. The reversal of 6643991808 is 8081993466.

It can be written as a sum of positive squares in 2 ways, for example, as 2833645824 + 3810345984 = 53232^2 + 61728^2 .

It is a super-2 number, since 2×6643991808² = 88285254289542217728, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6643991803) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 94908 + ... + 149316.

It is an arithmetic number, because the mean of its divisors is an integer number (180722815).

Almost surely, 2^6643991808 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 6643991808, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (9759032010).

6643991808 is an abundant number, since it is smaller than the sum of its proper divisors (12874072212).

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

6643991808 is a wasteful number, since it uses less digits than its factorization.

6643991808 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 54484 (or 54467 counting only the distinct ones).

The product of its (nonzero) digits is 2239488, while the sum is 54.

The square root of 6643991808 is about 81510.6852381944. The cubic root of 6643991808 is about 1879.9358481203.

The spelling of 6643991808 in words is "six billion, six hundred forty-three million, nine hundred ninety-one thousand, eight hundred eight".