218181 has 4 divisors (see below), whose sum is σ = 290912. Its totient is φ = 145452.

The previous prime is 218171. The next prime is 218191. The reversal of 218181 is 181812.

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.

It is an interprime number because it is at equal distance from previous prime (218171) and next prime (218191).

It is not a de Polignac number, because 218181 - 2⁵ = 218149 is a prime.

It is a super-2 number, since 2×218181² = 95205897522, which contains 22 as substring.

It is a D-number.

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

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (218111) 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, 36361 + ... + 36366.

It is an arithmetic number, because the mean of its divisors is an integer number (72728).

2²¹⁸¹⁸¹ is an apocalyptic number.

It is an amenable number.

218181 is a deficient number, since it is larger than the sum of its proper divisors (72731).

218181 is an equidigital number, since it uses as much as digits as its factorization.

218181 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 72730.

The product of its digits is 128, while the sum is 21.

The square root of 218181 is about 467.0984906848. The cubic root of 218181 is about 60.2012685391.

Adding to 218181 its reverse (181812), we get a palindrome (399993).

The spelling of 218181 in words is "two hundred eighteen thousand, one hundred eighty-one".