218555221 has 4 divisors (see below), whose sum is σ = 220489452. Its totient is φ = 216620992.

The previous prime is 218555209. The next prime is 218555231. The reversal of 218555221 is 122555812.

218555221 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 78960996 + 139594225 = 8886^2 + 11815^2 .

It is a cyclic number.

It is not a de Polignac number, because 218555221 - 2⁹ = 218554709 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (218555231) 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, 966946 + ... + 967171.

It is an arithmetic number, because the mean of its divisors is an integer number (55122363).

Almost surely, 2^218555221 is an apocalyptic number.

It is an amenable number.

218555221 is a deficient number, since it is larger than the sum of its proper divisors (1934231).

218555221 is a wasteful number, since it uses less digits than its factorization.

218555221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1934230.

The product of its digits is 8000, while the sum is 31.

The square root of 218555221 is about 14783.6132592814. The cubic root of 218555221 is about 602.3566767093.

The spelling of 218555221 in words is "two hundred eighteen million, five hundred fifty-five thousand, two hundred twenty-one".