18282721 has 4 divisors (see below), whose sum is σ = 18627732. Its totient is φ = 17937712.

The previous prime is 18282683. The next prime is 18282739. The reversal of 18282721 is 12728281.

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 15171025 + 3111696 = 3895^2 + 1764^2 .

It is a cyclic number.

It is not a de Polignac number, because 18282721 - 2¹¹ = 18280673 is a prime.

It is a super-3 number, since 3×18282721³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18282751) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 172426 + ... + 172531.

It is an arithmetic number, because the mean of its divisors is an integer number (4656933).

Almost surely, 2^18282721 is an apocalyptic number.

It is an amenable number.

18282721 is a deficient number, since it is larger than the sum of its proper divisors (345011).

18282721 is an equidigital number, since it uses as much as digits as its factorization.

18282721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 345010.

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

The square root of 18282721 is about 4275.8298609744. The cubic root of 18282721 is about 263.4391262511.

The spelling of 18282721 in words is "eighteen million, two hundred eighty-two thousand, seven hundred twenty-one".