21204405 has 12 divisors (see below), whose sum is σ = 36754380. Its totient is φ = 11308992.

The previous prime is 21204397. The next prime is 21204419. The reversal of 21204405 is 50440212.

It can be written as a sum of positive squares in 2 ways, for example, as 4704561 + 16499844 = 2169^2 + 4062^2 .

It is not a de Polignac number, because 21204405 - 2³ = 21204397 is a prime.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 235560 + ... + 235649.

It is an arithmetic number, because the mean of its divisors is an integer number (3062865).

Almost surely, 2^21204405 is an apocalyptic number.

It is an amenable number.

21204405 is a deficient number, since it is larger than the sum of its proper divisors (15549975).

21204405 is a wasteful number, since it uses less digits than its factorization.

21204405 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 471220 (or 471217 counting only the distinct ones).

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

The square root of 21204405 is about 4604.8241008751. The cubic root of 21204405 is about 276.7846684585.

Adding to 21204405 its reverse (50440212), we get a palindrome (71644617).

It can be divided in two parts, 21204 and 405, that added together give a square (21609 = 147²).

The spelling of 21204405 in words is "twenty-one million, two hundred four thousand, four hundred five".