21243904 has 96 divisors (see below), whose sum is σ = 49533120. Its totient is φ = 9011200.

The previous prime is 21243857. The next prime is 21243907. The reversal of 21243904 is 40934212.

It is a super-2 number, since 2×21243904² = 902606914322432, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21243907) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 518124 + ... + 518164.

It is an arithmetic number, because the mean of its divisors is an integer number (515970).

Almost surely, 2^21243904 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21243904, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24766560).

21243904 is an abundant number, since it is smaller than the sum of its proper divisors (28289216).

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

21243904 is a wasteful number, since it uses less digits than its factorization.

21243904 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 97 (or 77 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 25.

The square root of 21243904 is about 4609.1109771842. The cubic root of 21243904 is about 276.9564242209.

The spelling of 21243904 in words is "twenty-one million, two hundred forty-three thousand, nine hundred four".