21538818 has 64 divisors (see below), whose sum is σ = 57600000. Its totient is φ = 5828112.

The previous prime is 21538789. The next prime is 21538841. The reversal of 21538818 is 81883512.

It is a Curzon number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 5683 + ... + 8681.

It is an arithmetic number, because the mean of its divisors is an integer number (900000).

Almost surely, 2^21538818 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21538818, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28800000).

21538818 is an abundant number, since it is smaller than the sum of its proper divisors (36061182).

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

21538818 is a wasteful number, since it uses less digits than its factorization.

21538818 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3036 (or 3030 counting only the distinct ones).

The product of its digits is 15360, while the sum is 36.

The square root of 21538818 is about 4640.9932126647. The cubic root of 21538818 is about 278.2321353531.

The spelling of 21538818 in words is "twenty-one million, five hundred thirty-eight thousand, eight hundred eighteen".