21211728 has 60 divisors (see below), whose sum is σ = 56335680. Its totient is φ = 6877248.

The previous prime is 21211721. The next prime is 21211769. The reversal of 21211728 is 82711212.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a junction number, because it is equal to n+sod(n) for n = 21211698 and 21211707.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21211721) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 88633 + ... + 88871.

It is an arithmetic number, because the mean of its divisors is an integer number (938928).

Almost surely, 2^21211728 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21211728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28167840).

21211728 is an abundant number, since it is smaller than the sum of its proper divisors (35123952).

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

21211728 is a wasteful number, since it uses less digits than its factorization.

21211728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 336 (or 287 counting only the distinct ones).

The product of its digits is 448, while the sum is 24.

The square root of 21211728 is about 4605.6191766146. The cubic root of 21211728 is about 276.8165275752.

The spelling of 21211728 in words is "twenty-one million, two hundred eleven thousand, seven hundred twenty-eight".