216691 has 4 divisors (see below), whose sum is σ = 217672. Its totient is φ = 215712.

The previous prime is 216679. The next prime is 216703. The reversal of 216691 is 196612.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is an interprime number because it is at equal distance from previous prime (216679) and next prime (216703).

It is a cyclic number.

It is not a de Polignac number, because 216691 - 2⁹ = 216179 is a prime.

It is the 466-th Hogben number.

It is a Duffinian number.

It is a nialpdrome in base 15.

It is not an unprimeable number, because it can be changed into a prime (216641) by changing a digit.

It is a nontrivial repunit in base 465.

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, 16 + ... + 658.

It is an arithmetic number, because the mean of its divisors is an integer number (54418).

2²¹⁶⁶⁹¹ is an apocalyptic number.

216691 is a deficient number, since it is larger than the sum of its proper divisors (981).

216691 is an equidigital number, since it uses as much as digits as its factorization.

216691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 980.

The product of its digits is 648, while the sum is 25.

The square root of 216691 is about 465.5008055847. The cubic root of 216691 is about 60.0639133753.

The spelling of 216691 in words is "two hundred sixteen thousand, six hundred ninety-one".