21307808 has 24 divisors (see below), whose sum is σ = 43398180. Its totient is φ = 10286080.

The previous prime is 21307807. The next prime is 21307813. The reversal of 21307808 is 80870312.

It can be written as a sum of positive squares in 2 ways, for example, as 21049744 + 258064 = 4588^2 + 508^2 .

It is a Harshad number since it is a multiple of its sum of digits (29).

It is not an unprimeable number, because it can be changed into a prime (21307807) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 10553 + ... + 12408.

Almost surely, 2^21307808 is an apocalyptic number.

It is an amenable number.

21307808 is an abundant number, since it is smaller than the sum of its proper divisors (22090372).

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

21307808 is a wasteful number, since it uses less digits than its factorization.

21307808 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23000 (or 22992 counting only the distinct ones).

The product of its (nonzero) digits is 2688, while the sum is 29.

The square root of 21307808 is about 4616.0381280921. The cubic root of 21307808 is about 277.2338513590.

The spelling of 21307808 in words is "twenty-one million, three hundred seven thousand, eight hundred eight".