18658721 has 2 divisors, whose sum is σ = 18658722. Its totient is φ = 18658720.

The previous prime is 18658711. The next prime is 18658751. The reversal of 18658721 is 12785681.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15124321 + 3534400 = 3889^2 + 1880^2 .

It is an emirp because it is prime and its reverse (12785681) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18658721 - 2⁶ = 18658657 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (18658711) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9329360 + 9329361.

It is an arithmetic number, because the mean of its divisors is an integer number (9329361).

Almost surely, 2^18658721 is an apocalyptic number.

It is an amenable number.

18658721 is a deficient number, since it is larger than the sum of its proper divisors (1).

18658721 is an equidigital number, since it uses as much as digits as its factorization.

18658721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 26880, while the sum is 38.

The square root of 18658721 is about 4319.5741688273. The cubic root of 18658721 is about 265.2328367774.

The spelling of 18658721 in words is "eighteen million, six hundred fifty-eight thousand, seven hundred twenty-one".