21728520 has 256 divisors, whose sum is σ = 82944000. Its totient is φ = 5011200.

The previous prime is 21728513. The next prime is 21728527. The reversal of 21728520 is 2582712.

It is an interprime number because it is at equal distance from previous prime (21728513) and next prime (21728527).

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21728527) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 368251 + ... + 368309.

It is an arithmetic number, because the mean of its divisors is an integer number (324000).

Almost surely, 2^21728520 is an apocalyptic number.

21728520 is a gapful number since it is divisible by the number (20) 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 21728520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (41472000).

21728520 is an abundant number, since it is smaller than the sum of its proper divisors (61215480).

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

21728520 is a wasteful number, since it uses less digits than its factorization.

21728520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 121 (or 111 counting only the distinct ones).

The product of its (nonzero) digits is 2240, while the sum is 27.

The square root of 21728520 is about 4661.3860599611. The cubic root of 21728520 is about 279.0465872026.

The spelling of 21728520 in words is "twenty-one million, seven hundred twenty-eight thousand, five hundred twenty".