18240821 has 4 divisors (see below), whose sum is σ = 18333612. Its totient is φ = 18148032.

The previous prime is 18240793. The next prime is 18240829. The reversal of 18240821 is 12804281.

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 17757796 + 483025 = 4214^2 + 695^2 .

It is a cyclic number.

It is not a de Polignac number, because 18240821 - 2⁶ = 18240757 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 (18240829) 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, 46100 + ... + 46493.

It is an arithmetic number, because the mean of its divisors is an integer number (4583403).

Almost surely, 2^18240821 is an apocalyptic number.

It is an amenable number.

18240821 is a deficient number, since it is larger than the sum of its proper divisors (92791).

18240821 is an equidigital number, since it uses as much as digits as its factorization.

18240821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 92790.

The product of its (nonzero) digits is 1024, while the sum is 26.

The square root of 18240821 is about 4270.9274168499. The cubic root of 18240821 is about 263.2377240191.

The spelling of 18240821 in words is "eighteen million, two hundred forty thousand, eight hundred twenty-one".