21681028 has 24 divisors (see below), whose sum is σ = 39916800. Its totient is φ = 10289760.

The previous prime is 21681007. The next prime is 21681029. The reversal of 21681028 is 82018612.

It is a junction number, because it is equal to n+sod(n) for n = 21680987 and 21681005.

It is not an unprimeable number, because it can be changed into a prime (21681029) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 4923 + ... + 8221.

It is an arithmetic number, because the mean of its divisors is an integer number (1663200).

Almost surely, 2^21681028 is an apocalyptic number.

It is an amenable number.

21681028 is a deficient number, since it is larger than the sum of its proper divisors (18235772).

21681028 is a wasteful number, since it uses less digits than its factorization.

21681028 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3387 (or 3385 counting only the distinct ones).

The product of its (nonzero) digits is 1536, while the sum is 28.

The square root of 21681028 is about 4656.2890803729. The cubic root of 21681028 is about 278.8431349722.

The spelling of 21681028 in words is "twenty-one million, six hundred eighty-one thousand, twenty-eight".