21818538 has 64 divisors (see below), whose sum is σ = 55883520. Its totient is φ = 6181056.

The previous prime is 21818521. The next prime is 21818539. The reversal of 21818538 is 83581812.

It is not an unprimeable number, because it can be changed into a prime (21818539) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 74320 + ... + 74612.

It is an arithmetic number, because the mean of its divisors is an integer number (873180).

Almost surely, 2^21818538 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21818538, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27941760).

21818538 is an abundant number, since it is smaller than the sum of its proper divisors (34064982).

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

21818538 is a wasteful number, since it uses less digits than its factorization.

21818538 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 508 (or 502 counting only the distinct ones).

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

The square root of 21818538 is about 4671.0317917993. The cubic root of 21818538 is about 279.4314056642.

The spelling of 21818538 in words is "twenty-one million, eight hundred eighteen thousand, five hundred thirty-eight".