21015664 has 20 divisors (see below), whose sum is σ = 40807656. Its totient is φ = 10484672.

The previous prime is 21015649. The next prime is 21015671. The reversal of 21015664 is 46651012.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7842 + ... + 10174.

Almost surely, 2^21015664 is an apocalyptic number.

It is an amenable number.

21015664 is a deficient number, since it is larger than the sum of its proper divisors (19791992).

21015664 is a wasteful number, since it uses less digits than its factorization.

21015664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2904 (or 2898 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 25.

The square root of 21015664 is about 4584.2844588878. The cubic root of 21015664 is about 275.9609970791.

Adding to 21015664 its reverse (46651012), we get a palindrome (67666676).

The spelling of 21015664 in words is "twenty-one million, fifteen thousand, six hundred sixty-four".