21205504 has 40 divisors (see below), whose sum is σ = 42966000. Its totient is φ = 10454016.

The previous prime is 21205453. The next prime is 21205523. The reversal of 21205504 is 40550212.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 42247 + ... + 42745.

It is an arithmetic number, because the mean of its divisors is an integer number (1074150).

Almost surely, 2^21205504 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 21205504, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21483000).

21205504 is an abundant number, since it is smaller than the sum of its proper divisors (21760496).

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

21205504 is an frugal number, since it uses more digits than its factorization.

21205504 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 600 (or 584 counting only the distinct ones).

The product of its (nonzero) digits is 400, while the sum is 19.

The square root of 21205504 is about 4604.9434307057. The cubic root of 21205504 is about 276.7894501865.

Adding to 21205504 its reverse (40550212), we get a palindrome (61755716).

The spelling of 21205504 in words is "twenty-one million, two hundred five thousand, five hundred four".