21331664 has 20 divisors (see below), whose sum is σ = 41830656. Its totient is φ = 10536672.

The previous prime is 21331663. The next prime is 21331669. The reversal of 21331664 is 46613312.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21331663) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6704 + ... + 9359.

Almost surely, 2^21331664 is an apocalyptic number.

It is an amenable number.

21331664 is a deficient number, since it is larger than the sum of its proper divisors (20498992).

21331664 is a wasteful number, since it uses less digits than its factorization.

21331664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16154 (or 16148 counting only the distinct ones).

The product of its digits is 2592, while the sum is 26.

The square root of 21331664 is about 4618.6214393475. The cubic root of 21331664 is about 277.3372754823.

Adding to 21331664 its reverse (46613312), we get a palindrome (67944976).

The spelling of 21331664 in words is "twenty-one million, three hundred thirty-one thousand, six hundred sixty-four".