18665821 has 4 divisors (see below), whose sum is σ = 19309500. Its totient is φ = 18022144.

The previous prime is 18665819. The next prime is 18665833. The reversal of 18665821 is 12856681.

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 10797796 + 7868025 = 3286^2 + 2805^2 .

It is a cyclic number.

It is not a de Polignac number, because 18665821 - 2¹ = 18665819 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18665851) by changing a digit.

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, 321796 + ... + 321853.

It is an arithmetic number, because the mean of its divisors is an integer number (4827375).

Almost surely, 2^18665821 is an apocalyptic number.

It is an amenable number.

18665821 is a deficient number, since it is larger than the sum of its proper divisors (643679).

18665821 is an equidigital number, since it uses as much as digits as its factorization.

18665821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 643678.

The product of its digits is 23040, while the sum is 37.

The square root of 18665821 is about 4320.3959309304. The cubic root of 18665821 is about 265.2664745659.

The spelling of 18665821 in words is "eighteen million, six hundred sixty-five thousand, eight hundred twenty-one".