18728321 has 2 divisors, whose sum is σ = 18728322. Its totient is φ = 18728320.

The previous prime is 18728291. The next prime is 18728323. The reversal of 18728321 is 12382781.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12503296 + 6225025 = 3536^2 + 2495^2 .

It is an emirp because it is prime and its reverse (12382781) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18728321 - 2¹⁰ = 18727297 is a prime.

Together with 18728323, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (18728323) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9364160 + 9364161.

It is an arithmetic number, because the mean of its divisors is an integer number (9364161).

Almost surely, 2^18728321 is an apocalyptic number.

It is an amenable number.

18728321 is a deficient number, since it is larger than the sum of its proper divisors (1).

18728321 is an equidigital number, since it uses as much as digits as its factorization.

18728321 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5376, while the sum is 32.

The square root of 18728321 is about 4327.6230196264. The cubic root of 18728321 is about 265.5622144755.

The spelling of 18728321 in words is "eighteen million, seven hundred twenty-eight thousand, three hundred twenty-one".