18009521 has 2 divisors, whose sum is σ = 18009522. Its totient is φ = 18009520.

The previous prime is 18009503. The next prime is 18009527. The reversal of 18009521 is 12590081.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17305600 + 703921 = 4160^2 + 839^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18009521 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (18009527) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9004760 + 9004761.

It is an arithmetic number, because the mean of its divisors is an integer number (9004761).

Almost surely, 2^18009521 is an apocalyptic number.

It is an amenable number.

18009521 is a deficient number, since it is larger than the sum of its proper divisors (1).

18009521 is an equidigital number, since it uses as much as digits as its factorization.

18009521 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 720, while the sum is 26.

The square root of 18009521 is about 4243.7625993922. The cubic root of 18009521 is about 262.1203388296.

The spelling of 18009521 in words is "eighteen million, nine thousand, five hundred twenty-one".