21493209 has 8 divisors (see below), whose sum is σ = 28719360. Its totient is φ = 14297936.

The previous prime is 21493193. The next prime is 21493217. The reversal of 21493209 is 90239412.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21493209 - 2⁴ = 21493193 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21493229) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6042 + ... + 8915.

It is an arithmetic number, because the mean of its divisors is an integer number (3589920).

Almost surely, 2^21493209 is an apocalyptic number.

It is an amenable number.

21493209 is a deficient number, since it is larger than the sum of its proper divisors (7226151).

21493209 is a wasteful number, since it uses less digits than its factorization.

21493209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15439.

The product of its (nonzero) digits is 3888, while the sum is 30.

The square root of 21493209 is about 4636.0768975503. The cubic root of 21493209 is about 278.0356086748.

The spelling of 21493209 in words is "twenty-one million, four hundred ninety-three thousand, two hundred nine".