21321804 has 72 divisors (see below), whose sum is σ = 58664704. Its totient is φ = 5904000.

The previous prime is 21321803. The next prime is 21321809. The reversal of 21321804 is 40812312.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21321803) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 141129 + ... + 141279.

Almost surely, 2^21321804 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 21321804, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29332352).

21321804 is an abundant number, since it is smaller than the sum of its proper divisors (37342900).

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

21321804 is a wasteful number, since it uses less digits than its factorization.

21321804 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 247 (or 204 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 21.

The square root of 21321804 is about 4617.5538978988. The cubic root of 21321804 is about 277.2945382792.

The spelling of 21321804 in words is "twenty-one million, three hundred twenty-one thousand, eight hundred four".