216681 has 4 divisors (see below), whose sum is σ = 288912. Its totient is φ = 144452.

The previous prime is 216679. The next prime is 216703. The reversal of 216681 is 186612.

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 216681 - 2¹ = 216679 is a prime.

It is a super-2 number, since 2×216681² = 93901311522, which contains 22 as substring.

It is a D-number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 216681.

It is not an unprimeable number, because it can be changed into a prime (216641) 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, 36111 + ... + 36116.

It is an arithmetic number, because the mean of its divisors is an integer number (72228).

2²¹⁶⁶⁸¹ is an apocalyptic number.

It is an amenable number.

216681 is a deficient number, since it is larger than the sum of its proper divisors (72231).

216681 is an equidigital number, since it uses as much as digits as its factorization.

216681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 72230.

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

The square root of 216681 is about 465.4900643408. The cubic root of 216681 is about 60.0629894047.

The spelling of 216681 in words is "two hundred sixteen thousand, six hundred eighty-one".