21809304 has 128 divisors (see below), whose sum is σ = 67564800. Its totient is φ = 6462720.

The previous prime is 21809303. The next prime is 21809327. The reversal of 21809304 is 40390812.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21809303) 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, 159124 + ... + 159260.

It is an arithmetic number, because the mean of its divisors is an integer number (527850).

Almost surely, 2^21809304 is an apocalyptic number.

21809304 is a gapful number since it is divisible by the number (24) 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 21809304, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33782400).

21809304 is an abundant number, since it is smaller than the sum of its proper divisors (45755496).

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

21809304 is a wasteful number, since it uses less digits than its factorization.

21809304 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 230 (or 220 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 21809304 is about 4670.0432546177. The cubic root of 21809304 is about 279.3919799598.

The spelling of 21809304 in words is "twenty-one million, eight hundred nine thousand, three hundred four".