21309408 has 72 divisors (see below), whose sum is σ = 63253008. Its totient is φ = 6792192.

The previous prime is 21309401. The next prime is 21309433. The reversal of 21309408 is 80490312.

It is a tau number, because it is divible by the number of its divisors (72).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21309401) by changing a digit.

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 11 ways as a sum of consecutive naturals, for example, 5016 + ... + 8232.

It is an arithmetic number, because the mean of its divisors is an integer number (878514).

Almost surely, 2^21309408 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 21309408, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31626504).

21309408 is an abundant number, since it is smaller than the sum of its proper divisors (41943600).

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

21309408 is a wasteful number, since it uses less digits than its factorization.

21309408 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3256 (or 3245 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 21309408 is about 4616.2114336326. The cubic root of 21309408 is about 277.2407903343.

The spelling of 21309408 in words is "twenty-one million, three hundred nine thousand, four hundred eight".