21520224 has 72 divisors (see below), whose sum is σ = 66771432. Its totient is φ = 6520320.

The previous prime is 21520207. The next prime is 21520229. The reversal of 21520224 is 42202512.

It is a tau number, because it is divible by the number of its divisors (72).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 21520197 and 21520206.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21520229) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 229 + ... + 6564.

It is an arithmetic number, because the mean of its divisors is an integer number (927381).

Almost surely, 2^21520224 is an apocalyptic number.

21520224 is a gapful number since it is divisible by the number (24) 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 21520224, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33385716).

21520224 is an abundant number, since it is smaller than the sum of its proper divisors (45251208).

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

21520224 is a wasteful number, since it uses less digits than its factorization.

21520224 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6820 (or 6809 counting only the distinct ones).

The product of its (nonzero) digits is 320, while the sum is 18.

The square root of 21520224 is about 4638.9895451488. The cubic root of 21520224 is about 278.1520483562.

Adding to 21520224 its reverse (42202512), we get a palindrome (63722736).

The spelling of 21520224 in words is "twenty-one million, five hundred twenty thousand, two hundred twenty-four".