21105205 has 16 divisors (see below), whose sum is σ = 27720000. Its totient is φ = 15298560.

The previous prime is 21105199. The next prime is 21105221. The reversal of 21105205 is 50250112.

It is not a de Polignac number, because 21105205 - 2³ = 21105197 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 27061 + ... + 27829.

It is an arithmetic number, because the mean of its divisors is an integer number (1732500).

Almost surely, 2^21105205 is an apocalyptic number.

It is an amenable number.

21105205 is a deficient number, since it is larger than the sum of its proper divisors (6614795).

21105205 is a wasteful number, since it uses less digits than its factorization.

21105205 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1284.

The product of its (nonzero) digits is 100, while the sum is 16.

The square root of 21105205 is about 4594.0401609041. The cubic root of 21105205 is about 276.3523688503.

Adding to 21105205 its reverse (50250112), we get a palindrome (71355317).

The spelling of 21105205 in words is "twenty-one million, one hundred five thousand, two hundred five".