21205404 has 36 divisors (see below), whose sum is σ = 58476600. Its totient is φ = 6425760.

The previous prime is 21205399. The next prime is 21205447. The reversal of 21205404 is 40450212.

21205404 is a `hidden beast` number, since 2 + 120 + 540 + 4 = 666.

It is a tau number, because it is divible by the number of its divisors (36).

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 pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 26379 + ... + 27170.

It is an arithmetic number, because the mean of its divisors is an integer number (1624350).

Almost surely, 2^21205404 is an apocalyptic number.

It is an amenable number.

21205404 is an abundant number, since it is smaller than the sum of its proper divisors (37271196).

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

21205404 is a wasteful number, since it uses less digits than its factorization.

21205404 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53570 (or 53565 counting only the distinct ones).

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

The square root of 21205404 is about 4604.9325727963. The cubic root of 21205404 is about 276.7890150953.

Adding to 21205404 its reverse (40450212), we get a palindrome (61655616).

It can be divided in two parts, 21205 and 404, that added together give a square (21609 = 147²).

The spelling of 21205404 in words is "twenty-one million, two hundred five thousand, four hundred four".