18000721 has 2 divisors, whose sum is σ = 18000722. Its totient is φ = 18000720.

The previous prime is 18000709. The next prime is 18000727. The reversal of 18000721 is 12700081.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14899600 + 3101121 = 3860^2 + 1761^2 .

It is an emirp because it is prime and its reverse (12700081) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18000721 - 2⁹ = 18000209 is a prime.

It is not a weakly prime, because it can be changed into another prime (18000727) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9000360 + 9000361.

It is an arithmetic number, because the mean of its divisors is an integer number (9000361).

Almost surely, 2^18000721 is an apocalyptic number.

It is an amenable number.

18000721 is a deficient number, since it is larger than the sum of its proper divisors (1).

18000721 is an equidigital number, since it uses as much as digits as its factorization.

18000721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 112, while the sum is 19.

The square root of 18000721 is about 4242.7256569333. The cubic root of 18000721 is about 262.0776385493.

It can be divided in two parts, 18000 and 721, that added together give a triangular number (18721 = T₁₉₃).

The spelling of 18000721 in words is "eighteen million, seven hundred twenty-one", and thus it is an aban number.