221865 has 16 divisors (see below), whose sum is σ = 405888. Its totient is φ = 101376.

The previous prime is 221849. The next prime is 221873. The reversal of 221865 is 568122.

221865 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 221865 - 2⁴ = 221849 is a prime.

It is a Curzon number.

221865 is a lucky number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 952 + ... + 1161.

It is an arithmetic number, because the mean of its divisors is an integer number (25368).

2²²¹⁸⁶⁵ is an apocalyptic number.

It is an amenable number.

221865 is a deficient number, since it is larger than the sum of its proper divisors (184023).

221865 is a wasteful number, since it uses less digits than its factorization.

221865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2128.

The product of its digits is 960, while the sum is 24.

The square root of 221865 is about 471.0254770180. The cubic root of 221865 is about 60.5382132285.

Subtracting from 221865 its sum of digits (24), we obtain a square (221841 = 471²).

Adding to 221865 its reverse (568122), we get a palindrome (789987).

The spelling of 221865 in words is "two hundred twenty-one thousand, eight hundred sixty-five".