18181221 has 8 divisors (see below), whose sum is σ = 25023744. Its totient is φ = 11729760.

The previous prime is 18181213. The next prime is 18181243. The reversal of 18181221 is 12218181.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 18181221 - 2³ = 18181213 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 18181191 and 18181200.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18181021) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 97656 + ... + 97841.

It is an arithmetic number, because the mean of its divisors is an integer number (3127968).

Almost surely, 2^18181221 is an apocalyptic number.

It is an amenable number.

18181221 is a deficient number, since it is larger than the sum of its proper divisors (6842523).

18181221 is a wasteful number, since it uses less digits than its factorization.

18181221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 195531.

The product of its digits is 256, while the sum is 24.

The square root of 18181221 is about 4263.9443007619. The cubic root of 18181221 is about 262.9507104979.

The spelling of 18181221 in words is "eighteen million, one hundred eighty-one thousand, two hundred twenty-one".