18204721 has 4 divisors (see below), whose sum is σ = 18832500. Its totient is φ = 17576944.

The previous prime is 18204709. The next prime is 18204727. The reversal of 18204721 is 12740281.

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 8526400 + 9678321 = 2920^2 + 3111^2 .

It is a cyclic number.

It is not a de Polignac number, because 18204721 - 2⁵ = 18204689 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18204727) 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, 313846 + ... + 313903.

It is an arithmetic number, because the mean of its divisors is an integer number (4708125).

Almost surely, 2^18204721 is an apocalyptic number.

It is an amenable number.

18204721 is a deficient number, since it is larger than the sum of its proper divisors (627779).

18204721 is an equidigital number, since it uses as much as digits as its factorization.

18204721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 627778.

The product of its (nonzero) digits is 896, while the sum is 25.

The square root of 18204721 is about 4266.6990753977. The cubic root of 18204721 is about 263.0639533736.

The spelling of 18204721 in words is "eighteen million, two hundred four thousand, seven hundred twenty-one".