21530520 has 96 divisors (see below), whose sum is σ = 76349520. Its totient is φ = 5218560.

The previous prime is 21530513. The next prime is 21530527. The reversal of 21530520 is 2503512.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21530513) and next prime (21530527).

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 = 21530493 and 21530502.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21530527) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1242 + ... + 6678.

Almost surely, 2^21530520 is an apocalyptic number.

21530520 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 21530520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38174760).

21530520 is an abundant number, since it is smaller than the sum of its proper divisors (54819000).

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

21530520 is a wasteful number, since it uses less digits than its factorization.

21530520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5465 (or 5458 counting only the distinct ones).

The product of its (nonzero) digits is 300, while the sum is 18.

The square root of 21530520 is about 4640.0991368720. The cubic root of 21530520 is about 278.1964003867.

The spelling of 21530520 in words is "twenty-one million, five hundred thirty thousand, five hundred twenty".