6643981638 has 96 divisors (see below), whose sum is σ = 17232969600. Its totient is φ = 1891865808.

The previous prime is 6643981613. The next prime is 6643981639. The reversal of 6643981638 is 8361893466.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6643981639) 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 47 ways as a sum of consecutive naturals, for example, 808233 + ... + 816411.

It is an arithmetic number, because the mean of its divisors is an integer number (179510100).

Almost surely, 2^6643981638 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 6643981638, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (8616484800).

6643981638 is an abundant number, since it is smaller than the sum of its proper divisors (10588987962).

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

6643981638 is a wasteful number, since it uses less digits than its factorization.

6643981638 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8511 (or 8498 counting only the distinct ones).

The product of its digits is 4478976, while the sum is 54.

The square root of 6643981638 is about 81510.6228537115. The cubic root of 6643981638 is about 1879.9348889099.

The spelling of 6643981638 in words is "six billion, six hundred forty-three million, nine hundred eighty-one thousand, six hundred thirty-eight".