21139809 has 8 divisors (see below), whose sum is σ = 28289280. Its totient is φ = 14041776.

The previous prime is 21139793. The next prime is 21139813. The reversal of 21139809 is 90893112.

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

It is not a de Polignac number, because 21139809 - 2⁴ = 21139793 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21139809.

It is not an unprimeable number, because it can be changed into a prime (21139009) 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, 11889 + ... + 13550.

It is an arithmetic number, because the mean of its divisors is an integer number (3536160).

Almost surely, 2^21139809 is an apocalyptic number.

It is an amenable number.

21139809 is a deficient number, since it is larger than the sum of its proper divisors (7149471).

21139809 is a wasteful number, since it uses less digits than its factorization.

21139809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25719.

The product of its (nonzero) digits is 3888, while the sum is 33.

The square root of 21139809 is about 4597.8048022942. The cubic root of 21139809 is about 276.5033217503.

The spelling of 21139809 in words is "twenty-one million, one hundred thirty-nine thousand, eight hundred nine".