18356821 has 12 divisors (see below), whose sum is σ = 22610988. Its totient is φ = 14808192.

The previous prime is 18356803. The next prime is 18356827. The reversal of 18356821 is 12865381.

It can be written as a sum of positive squares in 2 ways, for example, as 7761796 + 10595025 = 2786^2 + 3255^2 .

It is not a de Polignac number, because 18356821 - 2²¹ = 16259669 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 (18356827) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 10186 + ... + 11851.

It is an arithmetic number, because the mean of its divisors is an integer number (1884249).

Almost surely, 2^18356821 is an apocalyptic number.

It is an amenable number.

18356821 is a deficient number, since it is larger than the sum of its proper divisors (4254167).

18356821 is a wasteful number, since it uses less digits than its factorization.

18356821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22068 (or 22061 counting only the distinct ones).

The product of its digits is 11520, while the sum is 34.

The square root of 18356821 is about 4284.4860835344. The cubic root of 18356821 is about 263.7945533923.

The spelling of 18356821 in words is "eighteen million, three hundred fifty-six thousand, eight hundred twenty-one".