1821665 has 4 divisors (see below), whose sum is σ = 2186004. Its totient is φ = 1457328.

The previous prime is 1821649. The next prime is 1821679. The reversal of 1821665 is 5661281.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 364816 + 1456849 = 604^2 + 1207^2 .

It is a cyclic number.

It is not a de Polignac number, because 1821665 - 2⁴ = 1821649 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 182162 + ... + 182171.

It is an arithmetic number, because the mean of its divisors is an integer number (546501).

2^1821665 is an apocalyptic number.

It is an amenable number.

1821665 is a deficient number, since it is larger than the sum of its proper divisors (364339).

1821665 is an equidigital number, since it uses as much as digits as its factorization.

1821665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 364338.

The product of its digits is 2880, while the sum is 29.

The square root of 1821665 is about 1349.6907053099. The cubic root of 1821665 is about 122.1301352575.

It can be divided in two parts, 18216 and 65, that added together give a palindrome (18281).

The spelling of 1821665 in words is "one million, eight hundred twenty-one thousand, six hundred sixty-five".