18212721 has 4 divisors (see below), whose sum is σ = 24283632. Its totient is φ = 12141812.

The previous prime is 18212683. The next prime is 18212731. The reversal of 18212721 is 12721281.

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.

It is a cyclic number.

It is not a de Polignac number, because 18212721 - 2⁶ = 18212657 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 18212691 and 18212700.

It is not an unprimeable number, because it can be changed into a prime (18212731) 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, 3035451 + ... + 3035456.

It is an arithmetic number, because the mean of its divisors is an integer number (6070908).

Almost surely, 2^18212721 is an apocalyptic number.

It is an amenable number.

18212721 is a deficient number, since it is larger than the sum of its proper divisors (6070911).

18212721 is an equidigital number, since it uses as much as digits as its factorization.

18212721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6070910.

The product of its digits is 448, while the sum is 24.

The square root of 18212721 is about 4267.6364653049. The cubic root of 18212721 is about 263.1024819038.

The spelling of 18212721 in words is "eighteen million, two hundred twelve thousand, seven hundred twenty-one".