216381 has 16 divisors (see below), whose sum is σ = 322560. Its totient is φ = 127920.

The previous prime is 216379. The next prime is 216397. The reversal of 216381 is 183612.

It is not a de Polignac number, because 216381 - 2¹ = 216379 is a prime.

It is a super-2 number, since 2×216381² = 93641474322, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 216381.

It is not an unprimeable number, because it can be changed into a prime (216371) 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 15 ways as a sum of consecutive naturals, for example, 2566 + ... + 2648.

It is an arithmetic number, because the mean of its divisors is an integer number (20160).

2²¹⁶³⁸¹ is an apocalyptic number.

216381 is the 249-th nonagonal number.

It is an amenable number.

216381 is a deficient number, since it is larger than the sum of its proper divisors (106179).

216381 is a wasteful number, since it uses less digits than its factorization.

216381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 176.

The product of its digits is 288, while the sum is 21.

The square root of 216381 is about 465.1677116912. The cubic root of 216381 is about 60.0352570561.

Adding to 216381 its reverse (183612), we get a palindrome (399993).

The spelling of 216381 in words is "two hundred sixteen thousand, three hundred eighty-one".