18221213 has 2 divisors, whose sum is σ = 18221214. Its totient is φ = 18221212.

The previous prime is 18221173. The next prime is 18221233. The reversal of 18221213 is 31212281.

It is an a-pointer prime, because the next prime (18221233) can be obtained adding 18221213 to its sum of digits (20).

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18207289 + 13924 = 4267^2 + 118^2 .

It is a cyclic number.

It is not a de Polignac number, because 18221213 - 2¹² = 18217117 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18221233) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9110606 + 9110607.

It is an arithmetic number, because the mean of its divisors is an integer number (9110607).

Almost surely, 2^18221213 is an apocalyptic number.

It is an amenable number.

18221213 is a deficient number, since it is larger than the sum of its proper divisors (1).

18221213 is an equidigital number, since it uses as much as digits as its factorization.

18221213 is an evil number, because the sum of its binary digits is even.

The product of its digits is 192, while the sum is 20.

The square root of 18221213 is about 4268.6312794618. The cubic root of 18221213 is about 263.1433675960.

Adding to 18221213 its reverse (31212281), we get a palindrome (49433494).

The spelling of 18221213 in words is "eighteen million, two hundred twenty-one thousand, two hundred thirteen".