21805105 has 8 divisors (see below), whose sum is σ = 29904192. Its totient is φ = 14952048.

The previous prime is 21805079. The next prime is 21805117. The reversal of 21805105 is 50150812.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21805105 - 2⁵ = 21805073 is a prime.

It is a super-2 number, since 2×21805105² = 950925208122050, which contains 22 as substring.

It is a Duffinian 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 7 ways as a sum of consecutive naturals, for example, 311467 + ... + 311536.

It is an arithmetic number, because the mean of its divisors is an integer number (3738024).

Almost surely, 2^21805105 is an apocalyptic number.

It is an amenable number.

21805105 is a deficient number, since it is larger than the sum of its proper divisors (8099087).

21805105 is an equidigital number, since it uses as much as digits as its factorization.

21805105 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 623015.

The product of its (nonzero) digits is 400, while the sum is 22.

The square root of 21805105 is about 4669.5936654060. The cubic root of 21805105 is about 279.3740481294.

Adding to 21805105 its reverse (50150812), we get a palindrome (71955917).

The spelling of 21805105 in words is "twenty-one million, eight hundred five thousand, one hundred five".