21288816 has 120 divisors (see below), whose sum is σ = 64995840. Its totient is φ = 6480000.

The previous prime is 21288779. The next prime is 21288829. The reversal of 21288816 is 61888212.

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is a Harshad number since it is a multiple of its sum of digits (36).

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 polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 84691 + ... + 84941.

It is an arithmetic number, because the mean of its divisors is an integer number (541632).

Almost surely, 2^21288816 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 21288816, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32497920).

21288816 is an abundant number, since it is smaller than the sum of its proper divisors (43707024).

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

21288816 is a wasteful number, since it uses less digits than its factorization.

21288816 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 315 (or 306 counting only the distinct ones).

The product of its digits is 12288, while the sum is 36.

The square root of 21288816 is about 4613.9804941070. The cubic root of 21288816 is about 277.1514591766.

The spelling of 21288816 in words is "twenty-one million, two hundred eighty-eight thousand, eight hundred sixteen".