21210209 has 8 divisors (see below), whose sum is σ = 22234560. Its totient is φ = 20194416.

The previous prime is 21210197. The next prime is 21210221. The reversal of 21210209 is 90201212.

It is an interprime number because it is at equal distance from previous prime (21210197) and next prime (21210221).

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 21210209 - 2⁴ = 21210193 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21210269) 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, 3254 + ... + 7280.

It is an arithmetic number, because the mean of its divisors is an integer number (2779320).

Almost surely, 2^21210209 is an apocalyptic number.

It is an amenable number.

21210209 is a deficient number, since it is larger than the sum of its proper divisors (1024351).

21210209 is a wasteful number, since it uses less digits than its factorization.

21210209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4279.

The product of its (nonzero) digits is 72, while the sum is 17.

The square root of 21210209 is about 4605.4542664106. The cubic root of 21210209 is about 276.8099196844.

The spelling of 21210209 in words is "twenty-one million, two hundred ten thousand, two hundred nine".