18111721 has 4 divisors (see below), whose sum is σ = 18120592. Its totient is φ = 18102852.

The previous prime is 18111713. The next prime is 18111727. The reversal of 18111721 is 12711181.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 12711181 = 7 ⋅1815883.

It is a cyclic number.

It is not a de Polignac number, because 18111721 - 2³ = 18111713 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 18111692 and 18111701.

It is not an unprimeable number, because it can be changed into a prime (18111727) 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, 346 + ... + 6028.

It is an arithmetic number, because the mean of its divisors is an integer number (4530148).

Almost surely, 2^18111721 is an apocalyptic number.

It is an amenable number.

18111721 is a deficient number, since it is larger than the sum of its proper divisors (8871).

18111721 is an equidigital number, since it uses as much as digits as its factorization.

18111721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8870.

The product of its digits is 112, while the sum is 22.

The square root of 18111721 is about 4255.7867662748. The cubic root of 18111721 is about 262.6152286250.

The spelling of 18111721 in words is "eighteen million, one hundred eleven thousand, seven hundred twenty-one".