216391 has 8 divisors (see below), whose sum is σ = 260480. Its totient is φ = 175608.

The previous prime is 216379. The next prime is 216397. The reversal of 216391 is 193612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 216391 - 2⁷ = 216263 is a prime.

It is a Duffinian number.

216391 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (216397) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 681 + ... + 946.

It is an arithmetic number, because the mean of its divisors is an integer number (32560).

2²¹⁶³⁹¹ is an apocalyptic number.

216391 is a deficient number, since it is larger than the sum of its proper divisors (44089).

216391 is a wasteful number, since it uses less digits than its factorization.

216391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1653.

The product of its digits is 324, while the sum is 22.

The square root of 216391 is about 465.1784603784. The cubic root of 216391 is about 60.0361818805.

The spelling of 216391 in words is "two hundred sixteen thousand, three hundred ninety-one".