20021209 has 8 divisors (see below), whose sum is σ = 21644672. Its totient is φ = 18409680.

The previous prime is 20021203. The next prime is 20021213. The reversal of 20021209 is 90212002.

It is a happy number.

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 20021209 - 2⁷ = 20021081 is a prime.

It is a super-3 number, since 3×20021209³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20021192 and 20021201.

It is not an unprimeable number, because it can be changed into a prime (20021203) 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, 682 + ... + 6364.

It is an arithmetic number, because the mean of its divisors is an integer number (2705584).

Almost surely, 2^20021209 is an apocalyptic number.

It is an amenable number.

20021209 is a deficient number, since it is larger than the sum of its proper divisors (1623463).

20021209 is a wasteful number, since it uses less digits than its factorization.

20021209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5967.

The product of its (nonzero) digits is 72, while the sum is 16.

The square root of 20021209 is about 4474.5065649745. The cubic root of 20021209 is about 271.5376779014.

The spelling of 20021209 in words is "twenty million, twenty-one thousand, two hundred nine".