21021520 has 160 divisors (see below), whose sum is σ = 59058720. Its totient is φ = 6881280.

The previous prime is 21021499. The next prime is 21021529. The reversal of 21021520 is 2512012.

It can be written as a sum of positive squares in 16 ways, for example, as 10419984 + 10601536 = 3228^2 + 3256^2 .

It is a super-2 number, since 2×21021520² = 883808606220800, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (13).

It is a self number, because there is not a number n which added to its sum of digits gives 21021520.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21021529) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 512700 + ... + 512740.

It is an arithmetic number, because the mean of its divisors is an integer number (369117).

Almost surely, 2^21021520 is an apocalyptic number.

21021520 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 21021520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29529360).

21021520 is an abundant number, since it is smaller than the sum of its proper divisors (38037200).

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

21021520 is a wasteful number, since it uses less digits than its factorization.

21021520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 113 (or 107 counting only the distinct ones).

The product of its (nonzero) digits is 40, while the sum is 13.

The square root of 21021520 is about 4584.9231182213. The cubic root of 21021520 is about 275.9866268112.

Adding to 21021520 its reverse (2512012), we get a palindrome (23533532).

The spelling of 21021520 in words is "twenty-one million, twenty-one thousand, five hundred twenty".