21005532 has 54 divisors (see below), whose sum is σ = 55556592. Its totient is φ = 6691344.

The previous prime is 21005503. The next prime is 21005539. The reversal of 21005532 is 23550012.

It is a happy number.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005539) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 18493 + ... + 19595.

Almost surely, 2^21005532 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 21005532, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27778296).

21005532 is an abundant number, since it is smaller than the sum of its proper divisors (34551060).

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

21005532 is a wasteful number, since it uses less digits than its factorization.

21005532 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1159 (or 1131 counting only the distinct ones).

The product of its (nonzero) digits is 300, while the sum is 18.

The square root of 21005532 is about 4583.1792458947. The cubic root of 21005532 is about 275.9166414930.

Adding to 21005532 its reverse (23550012), we get a palindrome (44555544).

The spelling of 21005532 in words is "twenty-one million, five thousand, five hundred thirty-two".