18042721 has 2 divisors, whose sum is σ = 18042722. Its totient is φ = 18042720.

The previous prime is 18042719. The next prime is 18042743. The reversal of 18042721 is 12724081.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 9834496 + 8208225 = 3136^2 + 2865^2 .

It is a cyclic number.

It is not a de Polignac number, because 18042721 - 2¹ = 18042719 is a prime.

It is a super-3 number, since 3×18042721³ (a number of 23 digits) contains 333 as substring.

Together with 18042719, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (18042781) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9021360 + 9021361.

It is an arithmetic number, because the mean of its divisors is an integer number (9021361).

Almost surely, 2^18042721 is an apocalyptic number.

It is an amenable number.

18042721 is a deficient number, since it is larger than the sum of its proper divisors (1).

18042721 is an equidigital number, since it uses as much as digits as its factorization.

18042721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 896, while the sum is 25.

The square root of 18042721 is about 4247.6724214562. The cubic root of 18042721 is about 262.2813102251.

The spelling of 18042721 in words is "eighteen million, forty-two thousand, seven hundred twenty-one".