21640209 has 8 divisors (see below), whose sum is σ = 28900800. Its totient is φ = 14403216.

The previous prime is 21640189. The next prime is 21640219. The reversal of 21640209 is 90204612.

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

It is not a de Polignac number, because 21640209 - 2⁷ = 21640081 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21640219) 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, 3634 + ... + 7515.

It is an arithmetic number, because the mean of its divisors is an integer number (3612600).

Almost surely, 2^21640209 is an apocalyptic number.

It is an amenable number.

21640209 is a deficient number, since it is larger than the sum of its proper divisors (7260591).

21640209 is a wasteful number, since it uses less digits than its factorization.

21640209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11799.

The product of its (nonzero) digits is 864, while the sum is 24.

The square root of 21640209 is about 4651.9038038205. The cubic root of 21640209 is about 278.6680318289.

The spelling of 21640209 in words is "twenty-one million, six hundred forty thousand, two hundred nine".