21205408 has 48 divisors (see below), whose sum is σ = 48129984. Its totient is φ = 9008640.

The previous prime is 21205399. The next prime is 21205447. The reversal of 21205408 is 80450212.

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, 30343 + ... + 31033.

It is an arithmetic number, because the mean of its divisors is an integer number (1002708).

Almost surely, 2^21205408 is an apocalyptic number.

21205408 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21205408, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24064992).

21205408 is an abundant number, since it is smaller than the sum of its proper divisors (26924576).

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

21205408 is a wasteful number, since it uses less digits than its factorization.

21205408 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 845 (or 837 counting only the distinct ones).

The product of its (nonzero) digits is 640, while the sum is 22.

The square root of 21205408 is about 4604.9330071131. The cubic root of 21205408 is about 276.7890324989.

The spelling of 21205408 in words is "twenty-one million, two hundred five thousand, four hundred eight".