21524220 has 72 divisors (see below), whose sum is σ = 65729664. Its totient is φ = 5701248.

The previous prime is 21524189. The next prime is 21524231. The reversal of 21524220 is 2242512.

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 = 21524193 and 21524202.

It is a congruent number.

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, 35157 + ... + 35763.

It is an arithmetic number, because the mean of its divisors is an integer number (912912).

Almost surely, 2^21524220 is an apocalyptic number.

21524220 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 21524220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32864832).

21524220 is an abundant number, since it is smaller than the sum of its proper divisors (44205444).

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

21524220 is a wasteful number, since it uses less digits than its factorization.

21524220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 819 (or 814 counting only the distinct ones).

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

The square root of 21524220 is about 4639.4202223985. The cubic root of 21524220 is about 278.1692635859.

Adding to 21524220 its reverse (2242512), we get a palindrome (23766732).

The spelling of 21524220 in words is "twenty-one million, five hundred twenty-four thousand, two hundred twenty".