21991824 has 100 divisors (see below), whose sum is σ = 64817280. Its totient is φ = 7197120.

The previous prime is 21991813. The next prime is 21991843. The reversal of 21991824 is 42819912.

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 an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 91897 + ... + 92135.

Almost surely, 2^21991824 is an apocalyptic number.

21991824 is a gapful number since it is divisible by the number (24) 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 21991824, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32408640).

21991824 is an abundant number, since it is smaller than the sum of its proper divisors (42825456).

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

21991824 is a wasteful number, since it uses less digits than its factorization.

21991824 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 330 (or 315 counting only the distinct ones).

The product of its digits is 10368, while the sum is 36.

The square root of 21991824 is about 4689.5441143036. The cubic root of 21991824 is about 280.1692174411.

The spelling of 21991824 in words is "twenty-one million, nine hundred ninety-one thousand, eight hundred twenty-four".