18204521 has 4 divisors (see below), whose sum is σ = 18453972. Its totient is φ = 17955072.

The previous prime is 18204499. The next prime is 18204539. The reversal of 18204521 is 12540281.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12540281 = 13 ⋅964637.

It can be written as a sum of positive squares in 2 ways, for example, as 11256025 + 6948496 = 3355^2 + 2636^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18204521 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18204551) 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, 124616 + ... + 124761.

It is an arithmetic number, because the mean of its divisors is an integer number (4613493).

Almost surely, 2^18204521 is an apocalyptic number.

It is an amenable number.

18204521 is a deficient number, since it is larger than the sum of its proper divisors (249451).

18204521 is an equidigital number, since it uses as much as digits as its factorization.

18204521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 249450.

The product of its (nonzero) digits is 640, while the sum is 23.

The square root of 18204521 is about 4266.6756380114. The cubic root of 18204521 is about 263.0629900158.

The spelling of 18204521 in words is "eighteen million, two hundred four thousand, five hundred twenty-one".