21005244 has 60 divisors (see below), whose sum is σ = 59147704. Its totient is φ = 6461856.

The previous prime is 21005227. The next prime is 21005269. The reversal of 21005244 is 44250012.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 1719 + ... + 6705.

Almost surely, 2^21005244 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 21005244, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29573852).

21005244 is an abundant number, since it is smaller than the sum of its proper divisors (38142460).

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

21005244 is a wasteful number, since it uses less digits than its factorization.

21005244 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5016 (or 5005 counting only the distinct ones).

The product of its (nonzero) digits is 320, while the sum is 18.

The square root of 21005244 is about 4583.1478265489. The cubic root of 21005244 is about 275.9153804862.

Adding to 21005244 its reverse (44250012), we get a palindrome (65255256).

The spelling of 21005244 in words is "twenty-one million, five thousand, two hundred forty-four".