21010209 has 8 divisors (see below), whose sum is σ = 30560352. Its totient is φ = 12733440.

The previous prime is 21010193. The next prime is 21010217. The reversal of 21010209 is 90201012.

It is a happy number.

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

It is not a de Polignac number, because 21010209 - 2⁴ = 21010193 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21010229) 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, 318304 + ... + 318369.

It is an arithmetic number, because the mean of its divisors is an integer number (3820044).

Almost surely, 2^21010209 is an apocalyptic number.

It is an amenable number.

21010209 is a deficient number, since it is larger than the sum of its proper divisors (9550143).

21010209 is a wasteful number, since it uses less digits than its factorization.

21010209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 636687.

The product of its (nonzero) digits is 36, while the sum is 15.

The square root of 21010209 is about 4583.6894528316. The cubic root of 21010209 is about 275.9371181047.

The spelling of 21010209 in words is "twenty-one million, ten thousand, two hundred nine".