21553728 has 168 divisors, whose sum is σ = 69494400. Its totient is φ = 5870592.

The previous prime is 21553717. The next prime is 21553787. The reversal of 21553728 is 82735512.

It is a tau number, because it is divible by the number of its divisors (168).

Its product of digits (16800) is a multiple of the sum of its prime divisors (120).

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 272793 + ... + 272871.

Almost surely, 2^21553728 is an apocalyptic number.

21553728 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 21553728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34747200).

21553728 is an abundant number, since it is smaller than the sum of its proper divisors (47940672).

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

21553728 is a wasteful number, since it uses less digits than its factorization.

21553728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 137 (or 120 counting only the distinct ones).

The product of its digits is 16800, while the sum is 33.

The square root of 21553728 is about 4642.5992719596. The cubic root of 21553728 is about 278.2963215473.

The spelling of 21553728 in words is "twenty-one million, five hundred fifty-three thousand, seven hundred twenty-eight".