18211521 has 4 divisors (see below), whose sum is σ = 24282032. Its totient is φ = 12141012.

The previous prime is 18211499. The next prime is 18211549. The reversal of 18211521 is 12511281.

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, and also an emirpimes, since its reverse is a distinct semiprime: 12511281 = 3 ⋅4170427.

It is not a de Polignac number, because 18211521 - 2¹⁰ = 18210497 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18211591) 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 3 ways as a sum of consecutive naturals, for example, 3035251 + ... + 3035256.

It is an arithmetic number, because the mean of its divisors is an integer number (6070508).

Almost surely, 2^18211521 is an apocalyptic number.

It is an amenable number.

18211521 is a deficient number, since it is larger than the sum of its proper divisors (6070511).

18211521 is an equidigital number, since it uses as much as digits as its factorization.

18211521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6070510.

The product of its digits is 160, while the sum is 21.

The square root of 18211521 is about 4267.4958699453. The cubic root of 18211521 is about 263.0967033437.

The spelling of 18211521 in words is "eighteen million, two hundred eleven thousand, five hundred twenty-one".