21812220 has 96 divisors (see below), whose sum is σ = 70103040. Its totient is φ = 5624640.

The previous prime is 21812213. The next prime is 21812221. The reversal of 21812220 is 2221812.

It is a happy number.

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 = 21812193 and 21812202.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21812221) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 16089 + ... + 17391.

It is an arithmetic number, because the mean of its divisors is an integer number (730240).

Almost surely, 2^21812220 is an apocalyptic number.

21812220 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 21812220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35051520).

21812220 is an abundant number, since it is smaller than the sum of its proper divisors (48290820).

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

21812220 is a wasteful number, since it uses less digits than its factorization.

21812220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1352 (or 1344 counting only the distinct ones).

The product of its (nonzero) digits is 128, while the sum is 18.

The square root of 21812220 is about 4670.3554468584. The cubic root of 21812220 is about 279.4044313843.

The spelling of 21812220 in words is "twenty-one million, eight hundred twelve thousand, two hundred twenty".