18221921 has 4 divisors (see below), whose sum is σ = 18280452. Its totient is φ = 18163392.

The previous prime is 18221899. The next prime is 18221953. The reversal of 18221921 is 12912281.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 4264225 + 13957696 = 2065^2 + 3736^2 .

It is a cyclic number.

It is not a de Polignac number, because 18221921 - 2¹⁰ = 18220897 is a prime.

It is not an unprimeable number, because it can be changed into a prime (18221821) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 28796 + ... + 29421.

It is an arithmetic number, because the mean of its divisors is an integer number (4570113).

Almost surely, 2^18221921 is an apocalyptic number.

It is an amenable number.

18221921 is a deficient number, since it is larger than the sum of its proper divisors (58531).

18221921 is an equidigital number, since it uses as much as digits as its factorization.

18221921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 58530.

The product of its digits is 576, while the sum is 26.

The square root of 18221921 is about 4268.7142092204. The cubic root of 18221921 is about 263.1467757681.

The spelling of 18221921 in words is "eighteen million, two hundred twenty-one thousand, nine hundred twenty-one".