21002001209 has 4 divisors (see below), whose sum is σ = 24002287104. Its totient is φ = 18001715316.

The previous prime is 21002001203. The next prime is 21002001217. The reversal of 21002001209 is 90210020012.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21002001209 - 2²⁸ = 20733565753 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21002001203) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1500142937 + ... + 1500142950.

It is an arithmetic number, because the mean of its divisors is an integer number (6000571776).

Almost surely, 2^21002001209 is an apocalyptic number.

It is an amenable number.

21002001209 is a deficient number, since it is larger than the sum of its proper divisors (3000285895).

21002001209 is an equidigital number, since it uses as much as digits as its factorization.

21002001209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3000285894.

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

The spelling of 21002001209 in words is "twenty-one billion, two million, one thousand, two hundred nine".