21105812 has 48 divisors (see below), whose sum is σ = 47453952. Its totient is φ = 7983360.

The previous prime is 21105811. The next prime is 21105863. The reversal of 21105812 is 21850112.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21105811) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7112 + ... + 9632.

It is an arithmetic number, because the mean of its divisors is an integer number (988624).

Almost surely, 2^21105812 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21105812, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23726976).

21105812 is an abundant number, since it is smaller than the sum of its proper divisors (26348140).

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

21105812 is a wasteful number, since it uses less digits than its factorization.

21105812 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2568 (or 2566 counting only the distinct ones).

The product of its (nonzero) digits is 160, while the sum is 20.

The square root of 21105812 is about 4594.1062242835. The cubic root of 21105812 is about 276.3550181854.

Adding to 21105812 its reverse (21850112), we get a palindrome (42955924).

The spelling of 21105812 in words is "twenty-one million, one hundred five thousand, eight hundred twelve".