18216221 has 2 divisors, whose sum is σ = 18216222. Its totient is φ = 18216220.

The previous prime is 18216181. The next prime is 18216223. The reversal of 18216221 is 12261281.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15100996 + 3115225 = 3886^2 + 1765^2 .

It is an emirp because it is prime and its reverse (12261281) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18216221 - 2⁶ = 18216157 is a prime.

Together with 18216223, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18216223) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9108110 + 9108111.

It is an arithmetic number, because the mean of its divisors is an integer number (9108111).

Almost surely, 2^18216221 is an apocalyptic number.

It is an amenable number.

18216221 is a deficient number, since it is larger than the sum of its proper divisors (1).

18216221 is an equidigital number, since it uses as much as digits as its factorization.

18216221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 384, while the sum is 23.

The square root of 18216221 is about 4268.0465086501. The cubic root of 18216221 is about 263.1193345880.

The spelling of 18216221 in words is "eighteen million, two hundred sixteen thousand, two hundred twenty-one".