21408816 has 80 divisors (see below), whose sum is σ = 64995840. Its totient is φ = 5986560.

The previous prime is 21408787. The next prime is 21408823. The reversal of 21408816 is 61880412.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5305 + ... + 8423.

It is an arithmetic number, because the mean of its divisors is an integer number (812448).

Almost surely, 2^21408816 is an apocalyptic number.

21408816 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21408816, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32497920).

21408816 is an abundant number, since it is smaller than the sum of its proper divisors (43587024).

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

21408816 is a wasteful number, since it uses less digits than its factorization.

21408816 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3154 (or 3148 counting only the distinct ones).

The product of its (nonzero) digits is 3072, while the sum is 30.

The square root of 21408816 is about 4626.9661766648. The cubic root of 21408816 is about 277.6712294412.

The spelling of 21408816 in words is "twenty-one million, four hundred eight thousand, eight hundred sixteen".