21221604 has 36 divisors (see below), whose sum is σ = 53858896. Its totient is φ = 7045488.

The previous prime is 21221597. The next prime is 21221621. The reversal of 21221604 is 40612212.

It is a tau number, because it is divible by the number of its divisors (36).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 9147 + ... + 11229.

Almost surely, 2^21221604 is an apocalyptic number.

It is an amenable number.

21221604 is an abundant number, since it is smaller than the sum of its proper divisors (32637292).

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

21221604 is a wasteful number, since it uses less digits than its factorization.

21221604 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2376 (or 2371 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 18.

The square root of 21221604 is about 4606.6912203880. The cubic root of 21221604 is about 276.8594820491.

Adding to 21221604 its reverse (40612212), we get a palindrome (61833816).

The spelling of 21221604 in words is "twenty-one million, two hundred twenty-one thousand, six hundred four".