21385728 has 320 divisors, whose sum is σ = 82494720. Its totient is φ = 5308416.

The previous prime is 21385717. The next prime is 21385733. The reversal of 21385728 is 82758312.

It is a Harshad number since it is a multiple of its sum of digits (36).

Its product of digits (26880) is a multiple of the sum of its prime divisors (42).

It is a junction number, because it is equal to n+sod(n) for n = 21385692 and 21385701.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1257976 + ... + 1257992.

It is an arithmetic number, because the mean of its divisors is an integer number (257796).

Almost surely, 2^21385728 is an apocalyptic number.

21385728 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 21385728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (41247360).

21385728 is an abundant number, since it is smaller than the sum of its proper divisors (61108992).

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

21385728 is a wasteful number, since it uses less digits than its factorization.

21385728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 64 (or 42 counting only the distinct ones).

The product of its digits is 26880, while the sum is 36.

The square root of 21385728 is about 4624.4705642917. The cubic root of 21385728 is about 277.5713768183.

The spelling of 21385728 in words is "twenty-one million, three hundred eighty-five thousand, seven hundred twenty-eight".