21681768 has 16 divisors (see below), whose sum is σ = 54204480. Its totient is φ = 7227248.

The previous prime is 21681739. The next prime is 21681769. The reversal of 21681768 is 86718612.

It is not an unprimeable number, because it can be changed into a prime (21681769) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 451680 + ... + 451727.

It is an arithmetic number, because the mean of its divisors is an integer number (3387780).

Almost surely, 2^21681768 is an apocalyptic number.

It is an amenable number.

21681768 is an abundant number, since it is smaller than the sum of its proper divisors (32522712).

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

21681768 is a wasteful number, since it uses less digits than its factorization.

21681768 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 903416 (or 903412 counting only the distinct ones).

The product of its digits is 32256, while the sum is 39.

The square root of 21681768 is about 4656.3685421152. The cubic root of 21681768 is about 278.8463073551.

The spelling of 21681768 in words is "twenty-one million, six hundred eighty-one thousand, seven hundred sixty-eight".