21684520 has 128 divisors (see below), whose sum is σ = 60963840. Its totient is φ = 6819840.

The previous prime is 21684517. The next prime is 21684521. The reversal of 21684520 is 2548612.

It is a hoax number, since the sum of its digits (28) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (21684521) 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, 97129 + ... + 97351.

It is an arithmetic number, because the mean of its divisors is an integer number (476280).

Almost surely, 2^21684520 is an apocalyptic number.

21684520 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 21684520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30481920).

21684520 is an abundant number, since it is smaller than the sum of its proper divisors (39279320).

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

21684520 is a wasteful number, since it uses less digits than its factorization.

21684520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 275 (or 271 counting only the distinct ones).

The product of its (nonzero) digits is 3840, while the sum is 28.

The square root of 21684520 is about 4656.6640419940. The cubic root of 21684520 is about 278.8581045569.

The spelling of 21684520 in words is "twenty-one million, six hundred eighty-four thousand, five hundred twenty".