21521604 has 96 divisors (see below), whose sum is σ = 58423680. Its totient is φ = 6110208.

The previous prime is 21521587. The next prime is 21521627. The reversal of 21521604 is 40612512.

It is a congruent number.

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, 157024 + ... + 157160.

It is an arithmetic number, because the mean of its divisors is an integer number (608580).

Almost surely, 2^21521604 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 21521604, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29211840).

21521604 is an abundant number, since it is smaller than the sum of its proper divisors (36902076).

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

21521604 is a wasteful number, since it uses less digits than its factorization.

21521604 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 229 (or 227 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 21.

The square root of 21521604 is about 4639.1382820520. The cubic root of 21521604 is about 278.1579937965.

The spelling of 21521604 in words is "twenty-one million, five hundred twenty-one thousand, six hundred four".