21220218 has 48 divisors (see below), whose sum is σ = 48746880. Its totient is φ = 6915456.

The previous prime is 21220211. The next prime is 21220219. The reversal of 21220218 is 81202212.

It is a happy number.

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

It is a self number, because there is not a number n which added to its sum of digits gives 21220218.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21220211) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 22378 + ... + 23306.

It is an arithmetic number, because the mean of its divisors is an integer number (1015560).

Almost surely, 2^21220218 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21220218, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24373440).

21220218 is an abundant number, since it is smaller than the sum of its proper divisors (27526662).

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

21220218 is an equidigital number, since it uses as much as digits as its factorization.

21220218 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 993 (or 981 counting only the distinct ones).

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

The square root of 21220218 is about 4606.5407845801. The cubic root of 21220218 is about 276.8534546128.

The spelling of 21220218 in words is "twenty-one million, two hundred twenty thousand, two hundred eighteen".