18345721 has 4 divisors (see below), whose sum is σ = 18424692. Its totient is φ = 18266752.

The previous prime is 18345709. The next prime is 18345727. The reversal of 18345721 is 12754381.

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 2433600 + 15912121 = 1560^2 + 3989^2 .

It is a cyclic number.

It is not a de Polignac number, because 18345721 - 2⁹ = 18345209 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18345727) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 39136 + ... + 39601.

It is an arithmetic number, because the mean of its divisors is an integer number (4606173).

Almost surely, 2^18345721 is an apocalyptic number.

It is an amenable number.

18345721 is a deficient number, since it is larger than the sum of its proper divisors (78971).

18345721 is an equidigital number, since it uses as much as digits as its factorization.

18345721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 78970.

The product of its digits is 6720, while the sum is 31.

The square root of 18345721 is about 4283.1905164258. The cubic root of 18345721 is about 263.7413722536.

The spelling of 18345721 in words is "eighteen million, three hundred forty-five thousand, seven hundred twenty-one".