218561 has 4 divisors (see below), whose sum is σ = 249792. Its totient is φ = 187332.

The previous prime is 218551. The next prime is 218579. The reversal of 218561 is 165812.

218561 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, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-218561 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 (218521) 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, 15605 + ... + 15618.

It is an arithmetic number, because the mean of its divisors is an integer number (62448).

2²¹⁸⁵⁶¹ is an apocalyptic number.

It is an amenable number.

218561 is a deficient number, since it is larger than the sum of its proper divisors (31231).

218561 is an equidigital number, since it uses as much as digits as its factorization.

218561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 31230.

The product of its digits is 480, while the sum is 23.

The square root of 218561 is about 467.5050801863. The cubic root of 218561 is about 60.2361985800.

The spelling of 218561 in words is "two hundred eighteen thousand, five hundred sixty-one".