21205320 has 32 divisors (see below), whose sum is σ = 63616320. Its totient is φ = 5654720.

The previous prime is 21205313. The next prime is 21205361. The reversal of 21205320 is 2350212.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a self number, because there is not a number n which added to its sum of digits gives 21205320.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 88236 + ... + 88475.

It is an arithmetic number, because the mean of its divisors is an integer number (1988010).

Almost surely, 2^21205320 is an apocalyptic number.

21205320 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21205320 is an abundant number, since it is smaller than the sum of its proper divisors (42411000).

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

21205320 is a wasteful number, since it uses less digits than its factorization.

21205320 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 176725 (or 176721 counting only the distinct ones).

The product of its (nonzero) digits is 120, while the sum is 15.

The square root of 21205320 is about 4604.9234521325. The cubic root of 21205320 is about 276.7886496175.

Adding to 21205320 its reverse (2350212), we get a palindrome (23555532).

The spelling of 21205320 in words is "twenty-one million, two hundred five thousand, three hundred twenty".