21538218 has 64 divisors (see below), whose sum is σ = 50561280. Its totient is φ = 6054912.

The previous prime is 21538169. The next prime is 21538219. The reversal of 21538218 is 81283512.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21538219) by changing a digit.

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 31 ways as a sum of consecutive naturals, for example, 48843 + ... + 49281.

It is an arithmetic number, because the mean of its divisors is an integer number (790020).

Almost surely, 2^21538218 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21538218, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25280640).

21538218 is an abundant number, since it is smaller than the sum of its proper divisors (29023062).

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

21538218 is a wasteful number, since it uses less digits than its factorization.

21538218 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 511.

The product of its digits is 3840, while the sum is 30.

The square root of 21538218 is about 4640.9285708789. The cubic root of 21538218 is about 278.2295517877.

The spelling of 21538218 in words is "twenty-one million, five hundred thirty-eight thousand, two hundred eighteen".