21013664 has 24 divisors (see below), whose sum is σ = 47281248. Its totient is φ = 9005760.

The previous prime is 21013633. The next prime is 21013709. The reversal of 21013664 is 46631012.

It is a happy number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 46682 + ... + 47129.

It is an arithmetic number, because the mean of its divisors is an integer number (1970052).

Almost surely, 2^21013664 is an apocalyptic number.

It is an amenable number.

21013664 is an abundant number, since it is smaller than the sum of its proper divisors (26267584).

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

21013664 is an equidigital number, since it uses as much as digits as its factorization.

21013664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 93828 (or 93820 counting only the distinct ones).

The product of its (nonzero) digits is 864, while the sum is 23.

The square root of 21013664 is about 4584.0663171468. The cubic root of 21013664 is about 275.9522426645.

Adding to 21013664 its reverse (46631012), we get a palindrome (67644676).

The spelling of 21013664 in words is "twenty-one million, thirteen thousand, six hundred sixty-four".