21811320 has 96 divisors (see below), whose sum is σ = 72586800. Its totient is φ = 5677056.

The previous prime is 21811261. The next prime is 21811351. The reversal of 21811320 is 2311812.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 21811293 and 21811302.

It is a congruent number.

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 23 ways as a sum of consecutive naturals, for example, 14776 + ... + 16184.

Almost surely, 2^21811320 is an apocalyptic number.

21811320 is a gapful number since it is divisible by the number (20) 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 21811320, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36293400).

21811320 is an abundant number, since it is smaller than the sum of its proper divisors (50775480).

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

21811320 is a wasteful number, since it uses less digits than its factorization.

21811320 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1469 (or 1462 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 18.

The square root of 21811320 is about 4670.2590934551. The cubic root of 21811320 is about 279.4005884705.

The spelling of 21811320 in words is "twenty-one million, eight hundred eleven thousand, three hundred twenty".