21791637728 has 144 divisors (see below), whose sum is σ = 50907346560. Its totient is φ = 8992409088.

The previous prime is 21791637709. The next prime is 21791637733. The reversal of 21791637728 is 82773619712.

It is a Harshad number since it is a multiple of its sum of digits (53).

It is a self number, because there is not a number n which added to its sum of digits gives 21791637728.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 37123451 + ... + 37124037.

It is an arithmetic number, because the mean of its divisors is an integer number (353523240).

Almost surely, 2^21791637728 is an apocalyptic number.

21791637728 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21791637728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25453673280).

21791637728 is an abundant number, since it is smaller than the sum of its proper divisors (29115708832).

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

21791637728 is an equidigital number, since it uses as much as digits as its factorization.

21791637728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 769 (or 708 counting only the distinct ones).

The product of its digits is 1778112, while the sum is 53.

The spelling of 21791637728 in words is "twenty-one billion, seven hundred ninety-one million, six hundred thirty-seven thousand, seven hundred twenty-eight".