21204420 has 48 divisors (see below), whose sum is σ = 59777088. Its totient is φ = 5616000.

The previous prime is 21204419. The next prime is 21204451. The reversal of 21204420 is 2440212.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a self number, because there is not a number n which added to its sum of digits gives 21204420.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8295 + ... + 10545.

It is an arithmetic number, because the mean of its divisors is an integer number (1245356).

Almost surely, 2^21204420 is an apocalyptic number.

21204420 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 21204420, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29888544).

21204420 is an abundant number, since it is smaller than the sum of its proper divisors (38572668).

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

21204420 is a wasteful number, since it uses less digits than its factorization.

21204420 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2420 (or 2418 counting only the distinct ones).

The product of its (nonzero) digits is 128, while the sum is 15.

The square root of 21204420 is about 4604.8257296015. The cubic root of 21204420 is about 276.7847337243.

Adding to 21204420 its reverse (2440212), we get a palindrome (23644632).

The spelling of 21204420 in words is "twenty-one million, two hundred four thousand, four hundred twenty".