21205835728 has 80 divisors (see below), whose sum is σ = 51271718400. Its totient is φ = 8254396800.

The previous prime is 21205835687. The next prime is 21205835741. The reversal of 21205835728 is 82753850212.

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, 1435323 + ... + 1450021.

It is an arithmetic number, because the mean of its divisors is an integer number (640896480).

Almost surely, 2^21205835728 is an apocalyptic number.

21205835728 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 21205835728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25635859200).

21205835728 is an abundant number, since it is smaller than the sum of its proper divisors (30065882672).

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

21205835728 is a wasteful number, since it uses less digits than its factorization.

21205835728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15896 (or 15890 counting only the distinct ones).

The product of its (nonzero) digits is 268800, while the sum is 43.

The spelling of 21205835728 in words is "twenty-one billion, two hundred five million, eight hundred thirty-five thousand, seven hundred twenty-eight".