216861 has 4 divisors (see below), whose sum is σ = 289152. Its totient is φ = 144572.

The previous prime is 216859. The next prime is 216877. The reversal of 216861 is 168612.

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 not a de Polignac number, because 216861 - 2¹ = 216859 is a prime.

It is a D-number.

It is a Curzon number.

216861 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (216841) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 36141 + ... + 36146.

It is an arithmetic number, because the mean of its divisors is an integer number (72288).

2²¹⁶⁸⁶¹ is an apocalyptic number.

It is an amenable number.

216861 is a deficient number, since it is larger than the sum of its proper divisors (72291).

216861 is an equidigital number, since it uses as much as digits as its factorization.

216861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 72290.

The product of its digits is 576, while the sum is 24.

The square root of 216861 is about 465.6833688248. The cubic root of 216861 is about 60.0796165290.

The spelling of 216861 in words is "two hundred sixteen thousand, eight hundred sixty-one".