18228721 has 8 divisors (see below), whose sum is σ = 20887040. Its totient is φ = 15583968.

The previous prime is 18228703. The next prime is 18228797. The reversal of 18228721 is 12782281.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 18228721 - 2⁷ = 18228593 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18228701) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 321 + ... + 6046.

It is an arithmetic number, because the mean of its divisors is an integer number (2610880).

Almost surely, 2^18228721 is an apocalyptic number.

It is an amenable number.

18228721 is a deficient number, since it is larger than the sum of its proper divisors (2658319).

18228721 is an equidigital number, since it uses as much as digits as its factorization.

18228721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6783.

The product of its digits is 3584, while the sum is 31.

The square root of 18228721 is about 4269.5106276949. The cubic root of 18228721 is about 263.1795051299.

The spelling of 18228721 in words is "eighteen million, two hundred twenty-eight thousand, seven hundred twenty-one".