21018816 has 168 divisors, whose sum is σ = 74334624. Its totient is φ = 5529600.

The previous prime is 21018799. The next prime is 21018821. The reversal of 21018816 is 61881012.

It is a tau number, because it is divible by the number of its divisors (168).

It is a self number, because there is not a number n which added to its sum of digits gives 21018816.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 52216 + ... + 52616.

It is an arithmetic number, because the mean of its divisors is an integer number (442468).

Almost surely, 2^21018816 is an apocalyptic number.

21018816 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 21018816, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37167312).

21018816 is an abundant number, since it is smaller than the sum of its proper divisors (53315808).

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

21018816 is a wasteful number, since it uses less digits than its factorization.

21018816 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 439 (or 426 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 27.

The square root of 21018816 is about 4584.6282292025. The cubic root of 21018816 is about 275.9747929090.

Adding to 21018816 its reverse (61881012), we get a palindrome (82899828).

The spelling of 21018816 in words is "twenty-one million, eighteen thousand, eight hundred sixteen".