18718321 has 2 divisors, whose sum is σ = 18718322. Its totient is φ = 18718320.

The previous prime is 18718319. The next prime is 18718351. The reversal of 18718321 is 12381781.

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., 14861025 + 3857296 = 3855^2 + 1964^2 .

It is an emirp because it is prime and its reverse (12381781) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18718321 - 2¹ = 18718319 is a prime.

Together with 18718319, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (18718351) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9359160 + 9359161.

It is an arithmetic number, because the mean of its divisors is an integer number (9359161).

Almost surely, 2^18718321 is an apocalyptic number.

It is an amenable number.

18718321 is a deficient number, since it is larger than the sum of its proper divisors (1).

18718321 is an equidigital number, since it uses as much as digits as its factorization.

18718321 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2688, while the sum is 31.

The square root of 18718321 is about 4326.4674966998. The cubic root of 18718321 is about 265.5149403509.

The spelling of 18718321 in words is "eighteen million, seven hundred eighteen thousand, three hundred twenty-one".