21053904 has 20 divisors (see below), whose sum is σ = 54389376. Its totient is φ = 7017952.

The previous prime is 21053897. The next prime is 21053909. The reversal of 21053904 is 40935012.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21053909) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 219264 + ... + 219359.

Almost surely, 2^21053904 is an apocalyptic number.

21053904 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21053904 is an abundant number, since it is smaller than the sum of its proper divisors (33335472).

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

21053904 is a wasteful number, since it uses less digits than its factorization.

21053904 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 438634 (or 438628 counting only the distinct ones).

The product of its (nonzero) digits is 1080, while the sum is 24.

The square root of 21053904 is about 4588.4533341857. The cubic root of 21053904 is about 276.1282747569.

Adding to 21053904 its reverse (40935012), we get a palindrome (61988916).

The spelling of 21053904 in words is "twenty-one million, fifty-three thousand, nine hundred four".