21305808 has 80 divisors (see below), whose sum is σ = 61752000. Its totient is φ = 7032960.

The previous prime is 21305789. The next prime is 21305839. The reversal of 21305808 is 80850312.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (27).

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, 64203 + ... + 64533.

It is an arithmetic number, because the mean of its divisors is an integer number (771900).

Almost surely, 2^21305808 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21305808, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30876000).

21305808 is an abundant number, since it is smaller than the sum of its proper divisors (40446192).

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

21305808 is a wasteful number, since it uses less digits than its factorization.

21305808 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 497 (or 485 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 27.

The square root of 21305808 is about 4615.8214870162. The cubic root of 21305808 is about 277.2251771513.

The spelling of 21305808 in words is "twenty-one million, three hundred five thousand, eight hundred eight".