21805908 has 12 divisors (see below), whose sum is σ = 50880480. Its totient is φ = 7268632.

The previous prime is 21805907. The next prime is 21805933. The reversal of 21805908 is 80950812.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (12).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21805907) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 908568 + ... + 908591.

It is an arithmetic number, because the mean of its divisors is an integer number (4240040).

Almost surely, 2^21805908 is an apocalyptic number.

It is an amenable number.

21805908 is an abundant number, since it is smaller than the sum of its proper divisors (29074572).

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

21805908 is a wasteful number, since it uses less digits than its factorization.

21805908 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1817166 (or 1817164 counting only the distinct ones).

The product of its (nonzero) digits is 5760, while the sum is 33.

The square root of 21805908 is about 4669.6796463997. The cubic root of 21805908 is about 279.3774775191.

The spelling of 21805908 in words is "twenty-one million, eight hundred five thousand, nine hundred eight".