221861 has 4 divisors (see below), whose sum is σ = 223500. Its totient is φ = 220224.

The previous prime is 221849. The next prime is 221873. The reversal of 221861 is 168122.

221861 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 an emirpimes, since its reverse is a distinct semiprime: 168122 = 2 ⋅84061.

It is an interprime number because it is at equal distance from previous prime (221849) and next prime (221873).

It can be written as a sum of positive squares in 2 ways, for example, as 36100 + 185761 = 190^2 + 431^2 .

It is a cyclic number.

It is not a de Polignac number, because 221861 - 2⁶ = 221797 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (221831) 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, 596 + ... + 893.

It is an arithmetic number, because the mean of its divisors is an integer number (55875).

2²²¹⁸⁶¹ is an apocalyptic number.

It is an amenable number.

221861 is a deficient number, since it is larger than the sum of its proper divisors (1639).

221861 is a wasteful number, since it uses less digits than its factorization.

221861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1638.

The product of its digits is 192, while the sum is 20.

The square root of 221861 is about 471.0212309440. The cubic root of 221861 is about 60.5378494122.

Subtracting from 221861 its sum of digits (20), we obtain a square (221841 = 471²).

Adding to 221861 its reverse (168122), we get a palindrome (389983).

The spelling of 221861 in words is "two hundred twenty-one thousand, eight hundred sixty-one".