21105444 has 48 divisors (see below), whose sum is σ = 52512768. Its totient is φ = 6582048.

The previous prime is 21105443. The next prime is 21105457. The reversal of 21105444 is 44450112.

It is a happy number.

It is a self number, because there is not a number n which added to its sum of digits gives 21105444.

It is not an unprimeable number, because it can be changed into a prime (21105443) 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, 12159 + ... + 13785.

It is an arithmetic number, because the mean of its divisors is an integer number (1094016).

Almost surely, 2^21105444 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 21105444, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26256384).

21105444 is an abundant number, since it is smaller than the sum of its proper divisors (31407324).

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

21105444 is a wasteful number, since it uses less digits than its factorization.

21105444 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1704 (or 1702 counting only the distinct ones).

The product of its (nonzero) digits is 640, while the sum is 21.

The square root of 21105444 is about 4594.0661727929. The cubic root of 21105444 is about 276.3534120047.

Adding to 21105444 its reverse (44450112), we get a palindrome (65555556).

The spelling of 21105444 in words is "twenty-one million, one hundred five thousand, four hundred forty-four".