21408205 has 16 divisors (see below), whose sum is σ = 31618944. Its totient is φ = 13550400.

The previous prime is 21408181. The next prime is 21408227. The reversal of 21408205 is 50280412.

It is not a de Polignac number, because 21408205 - 2⁵ = 21408173 is a prime.

It is a super-2 number, since 2×21408205² = 916622482644050, which contains 22 as substring.

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 15 ways as a sum of consecutive naturals, for example, 23071 + ... + 23980.

It is an arithmetic number, because the mean of its divisors is an integer number (1976184).

Almost surely, 2^21408205 is an apocalyptic number.

It is an amenable number.

21408205 is a deficient number, since it is larger than the sum of its proper divisors (10210739).

21408205 is a wasteful number, since it uses less digits than its factorization.

21408205 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 47076.

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

The square root of 21408205 is about 4626.9001502086. The cubic root of 21408205 is about 277.6685878700.

Adding to 21408205 its reverse (50280412), we get a palindrome (71688617).

The spelling of 21408205 in words is "twenty-one million, four hundred eight thousand, two hundred five".