21004920 has 96 divisors (see below), whose sum is σ = 70827120. Its totient is φ = 5598720.

The previous prime is 21004913. The next prime is 21004931. The reversal of 21004920 is 2940012.

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 = 21004893 and 21004902.

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, 8640 + ... + 10800.

Almost surely, 2^21004920 is an apocalyptic number.

21004920 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 21004920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35413560).

21004920 is an abundant number, since it is smaller than the sum of its proper divisors (49822200).

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

21004920 is a wasteful number, since it uses less digits than its factorization.

21004920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2187 (or 2171 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 18.

The square root of 21004920 is about 4583.1124795274. The cubic root of 21004920 is about 275.9139618397.

Adding to 21004920 its reverse (2940012), we get a palindrome (23944932).

The spelling of 21004920 in words is "twenty-one million, four thousand, nine hundred twenty".