21309808 has 20 divisors (see below), whose sum is σ = 44464168. Its totient is φ = 9835200.

The previous prime is 21309793. The next prime is 21309829. The reversal of 21309808 is 80890312.

It is a self number, because there is not a number n which added to its sum of digits gives 21309808.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 51018 + ... + 51433.

Almost surely, 2^21309808 is an apocalyptic number.

It is an amenable number.

21309808 is an abundant number, since it is smaller than the sum of its proper divisors (23154360).

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

21309808 is a wasteful number, since it uses less digits than its factorization.

21309808 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 102472 (or 102466 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 31.

The square root of 21309808 is about 4616.2547590011. The cubic root of 21309808 is about 277.2425250238.

The spelling of 21309808 in words is "twenty-one million, three hundred nine thousand, eight hundred eight".