18821209 has 4 divisors (see below), whose sum is σ = 20532240. Its totient is φ = 17110180.

The previous prime is 18821161. The next prime is 18821213. The reversal of 18821209 is 90212881.

It is a happy number.

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 18821209 - 2¹³ = 18813017 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18821219) 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, 855499 + ... + 855520.

It is an arithmetic number, because the mean of its divisors is an integer number (5133060).

Almost surely, 2^18821209 is an apocalyptic number.

It is an amenable number.

18821209 is a deficient number, since it is larger than the sum of its proper divisors (1711031).

18821209 is a wasteful number, since it uses less digits than its factorization.

18821209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1711030.

The product of its (nonzero) digits is 2304, while the sum is 31.

The square root of 18821209 is about 4338.3417338887. The cubic root of 18821209 is about 266.0005323448. Note that the first 3 decimals are identical.

The spelling of 18821209 in words is "eighteen million, eight hundred twenty-one thousand, two hundred nine".