21664009 has 8 divisors (see below), whose sum is σ = 23540480. Its totient is φ = 19861200.

The previous prime is 21664007. The next prime is 21664037. The reversal of 21664009 is 90046612.

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 21664009 - 2¹ = 21664007 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21664007) 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, 17802 + ... + 18979.

It is an arithmetic number, because the mean of its divisors is an integer number (2942560).

Almost surely, 2^21664009 is an apocalyptic number.

It is an amenable number.

21664009 is a deficient number, since it is larger than the sum of its proper divisors (1876471).

21664009 is a wasteful number, since it uses less digits than its factorization.

21664009 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 36831.

The product of its (nonzero) digits is 2592, while the sum is 28.

The square root of 21664009 is about 4654.4611933069. The cubic root of 21664009 is about 278.7701545215.

The spelling of 21664009 in words is "twenty-one million, six hundred sixty-four thousand, nine".