1821209 has 8 divisors (see below), whose sum is σ = 2046912. Its totient is φ = 1607760.

The previous prime is 1821191. The next prime is 1821233. The reversal of 1821209 is 9021281.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1821209 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (23).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1821289) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2747 + ... + 3344.

It is an arithmetic number, because the mean of its divisors is an integer number (255864).

2^1821209 is an apocalyptic number.

It is an amenable number.

1821209 is a deficient number, since it is larger than the sum of its proper divisors (225703).

1821209 is a wasteful number, since it uses less digits than its factorization.

1821209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6127.

The product of its (nonzero) digits is 288, while the sum is 23.

The square root of 1821209 is about 1349.5217671457. The cubic root of 1821209 is about 122.1199438503.

Subtracting from 1821209 its sum of digits (23), we obtain a triangular number (1821186 = T₁₉₀₈).

The spelling of 1821209 in words is "one million, eight hundred twenty-one thousand, two hundred nine".