21821166 has 48 divisors (see below), whose sum is σ = 51807600. Its totient is φ = 6607104.

The previous prime is 21821153. The next prime is 21821171. The reversal of 21821166 is 66112812.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 7645 + ... + 10103.

It is an arithmetic number, because the mean of its divisors is an integer number (1079325).

Almost surely, 2^21821166 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21821166, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25903800).

21821166 is an abundant number, since it is smaller than the sum of its proper divisors (29986434).

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

21821166 is a wasteful number, since it uses less digits than its factorization.

21821166 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2513 (or 2510 counting only the distinct ones).

The product of its digits is 1152, while the sum is 27.

The square root of 21821166 is about 4671.3130916264. The cubic root of 21821166 is about 279.4426242016.

Adding to 21821166 its reverse (66112812), we get a palindrome (87933978).

The spelling of 21821166 in words is "twenty-one million, eight hundred twenty-one thousand, one hundred sixty-six".