21816816 has 80 divisors (see below), whose sum is σ = 66662400. Its totient is φ = 6015744.

The previous prime is 21816803. The next prime is 21816841. The reversal of 21816816 is 61861812.

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 8625 + ... + 10863.

It is an arithmetic number, because the mean of its divisors is an integer number (833280).

Almost surely, 2^21816816 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21816816, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33331200).

21816816 is an abundant number, since it is smaller than the sum of its proper divisors (44845584).

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

21816816 is a wasteful number, since it uses less digits than its factorization.

21816816 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2286 (or 2280 counting only the distinct ones).

The product of its digits is 4608, while the sum is 33.

The square root of 21816816 is about 4670.8474605793. The cubic root of 21816816 is about 279.4240542163.

The spelling of 21816816 in words is "twenty-one million, eight hundred sixteen thousand, eight hundred sixteen".