21604044 has 96 divisors (see below), whose sum is σ = 63737856. Its totient is φ = 5532480.

The previous prime is 21604031. The next prime is 21604057. The reversal of 21604044 is 44040612.

It is an interprime number because it is at equal distance from previous prime (21604031) and next prime (21604057).

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

It is a self number, because there is not a number n which added to its sum of digits gives 21604044.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 95059 + ... + 95285.

It is an arithmetic number, because the mean of its divisors is an integer number (663936).

Almost surely, 2^21604044 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 21604044, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31868928).

21604044 is an abundant number, since it is smaller than the sum of its proper divisors (42133812).

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

21604044 is a wasteful number, since it uses less digits than its factorization.

21604044 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 355 (or 353 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 21.

The square root of 21604044 is about 4648.0150602166. The cubic root of 21604044 is about 278.5127091037.

Adding to 21604044 its reverse (44040612), we get a palindrome (65644656).

The spelling of 21604044 in words is "twenty-one million, six hundred four thousand, forty-four".