18070721 has 4 divisors (see below), whose sum is σ = 18411732. Its totient is φ = 17729712.

The previous prime is 18070699. The next prime is 18070727. The reversal of 18070721 is 12707081.

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 6948496 + 11122225 = 2636^2 + 3335^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18070721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18070727) 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, 170426 + ... + 170531.

It is an arithmetic number, because the mean of its divisors is an integer number (4602933).

Almost surely, 2^18070721 is an apocalyptic number.

It is an amenable number.

18070721 is a deficient number, since it is larger than the sum of its proper divisors (341011).

18070721 is an equidigital number, since it uses as much as digits as its factorization.

18070721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 341010.

The product of its (nonzero) digits is 784, while the sum is 26.

The square root of 18070721 is about 4250.9670664450. The cubic root of 18070721 is about 262.4169158070.

The spelling of 18070721 in words is "eighteen million, seventy thousand, seven hundred twenty-one".