18221405 has 18 divisors (see below), whose sum is σ = 23136414. Its totient is φ = 13775344.

The previous prime is 18221393. The next prime is 18221407. The reversal of 18221405 is 50412281.

It can be written as a sum of positive squares in only one way, i.e., 14577124 + 3644281 = 3818^2 + 1909^2 .

It is not a de Polignac number, because 18221405 - 2⁴ = 18221389 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (23).

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18221407) 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 in 17 ways as a sum of consecutive naturals, for example, 219494 + ... + 219576.

Almost surely, 2^18221405 is an apocalyptic number.

It is an amenable number.

18221405 is a deficient number, since it is larger than the sum of its proper divisors (4915009).

18221405 is an frugal number, since it uses more digits than its factorization.

18221405 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 217 (or 111 counting only the distinct ones).

The product of its (nonzero) digits is 640, while the sum is 23.

The square root of 18221405 is about 4268.6537690471. The cubic root of 18221405 is about 263.1442918548.

Adding to 18221405 its reverse (50412281), we get a palindrome (68633686).

The spelling of 18221405 in words is "eighteen million, two hundred twenty-one thousand, four hundred five".