218921 has 4 divisors (see below), whose sum is σ = 226500. Its totient is φ = 211344.

The previous prime is 218887. The next prime is 218923. The reversal of 218921 is 129812.

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 151321 + 67600 = 389^2 + 260^2 .

It is a cyclic number.

It is not a de Polignac number, because 218921 - 2⁶ = 218857 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (218923) 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, 3746 + ... + 3803.

It is an arithmetic number, because the mean of its divisors is an integer number (56625).

2²¹⁸⁹²¹ is an apocalyptic number.

It is an amenable number.

218921 is a deficient number, since it is larger than the sum of its proper divisors (7579).

218921 is an equidigital number, since it uses as much as digits as its factorization.

218921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7578.

The product of its digits is 288, while the sum is 23.

The square root of 218921 is about 467.8899443245. The cubic root of 218921 is about 60.2692528704.

The spelling of 218921 in words is "two hundred eighteen thousand, nine hundred twenty-one".