18516221 has 4 divisors (see below), whose sum is σ = 18739392. Its totient is φ = 18293052.

The previous prime is 18516193. The next prime is 18516283. The reversal of 18516221 is 12261581.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 18516221 - 2¹⁸ = 18254077 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18516821) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 111461 + ... + 111626.

It is an arithmetic number, because the mean of its divisors is an integer number (4684848).

Almost surely, 2^18516221 is an apocalyptic number.

It is an amenable number.

18516221 is a deficient number, since it is larger than the sum of its proper divisors (223171).

18516221 is an equidigital number, since it uses as much as digits as its factorization.

18516221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 223170.

The product of its digits is 960, while the sum is 26.

The square root of 18516221 is about 4303.0478733103. The cubic root of 18516221 is about 264.5559002923. Note that the first 3 decimals are identical.

The spelling of 18516221 in words is "eighteen million, five hundred sixteen thousand, two hundred twenty-one".