21681568 has 24 divisors (see below), whose sum is σ = 42844032. Its totient is φ = 10800576.

The previous prime is 21681553. The next prime is 21681599. The reversal of 21681568 is 86518612.

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 3 ways as a sum of consecutive naturals, for example, 8721 + ... + 10927.

It is an arithmetic number, because the mean of its divisors is an integer number (1785168).

Almost surely, 2^21681568 is an apocalyptic number.

It is an amenable number.

21681568 is a deficient number, since it is larger than the sum of its proper divisors (21162464).

21681568 is a wasteful number, since it uses less digits than its factorization.

21681568 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2524 (or 2516 counting only the distinct ones).

The product of its digits is 23040, while the sum is 37.

The square root of 21681568 is about 4656.3470661024. The cubic root of 21681568 is about 278.8454499615.

The spelling of 21681568 in words is "twenty-one million, six hundred eighty-one thousand, five hundred sixty-eight".