21688816 has 20 divisors (see below), whose sum is σ = 43849872. Its totient is φ = 10372736.

The previous prime is 21688783. The next prime is 21688817. The reversal of 21688816 is 61888612.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21688817) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 29101 + ... + 29836.

Almost surely, 2^21688816 is an apocalyptic number.

It is an amenable number.

21688816 is an abundant number, since it is smaller than the sum of its proper divisors (22161056).

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

21688816 is a wasteful number, since it uses less digits than its factorization.

21688816 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 58968 (or 58962 counting only the distinct ones).

The product of its digits is 36864, while the sum is 40.

The square root of 21688816 is about 4657.1252935690. The cubic root of 21688816 is about 278.8765185424.

The spelling of 21688816 in words is "twenty-one million, six hundred eighty-eight thousand, eight hundred sixteen".