216581 has 4 divisors (see below), whose sum is σ = 228000. Its totient is φ = 205164.

The previous prime is 216577. The next prime is 216607. The reversal of 216581 is 185612.

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 216581 - 2² = 216577 is a prime.

It is a super-2 number, since 2×216581² = 93814659122, which contains 22 as substring.

It is an Ulam number.

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

It is a nialpdrome in base 13.

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 216581.

It is not an unprimeable number, because it can be changed into a prime (216551) 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, 5681 + ... + 5718.

It is an arithmetic number, because the mean of its divisors is an integer number (57000).

2²¹⁶⁵⁸¹ is an apocalyptic number.

It is an amenable number.

216581 is a deficient number, since it is larger than the sum of its proper divisors (11419).

216581 is a wasteful number, since it uses less digits than its factorization.

216581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11418.

The product of its digits is 480, while the sum is 23.

The square root of 216581 is about 465.3826382666. The cubic root of 216581 is about 60.0537481342.

It can be divided in two parts, 216 and 581, that added together give a palindrome (797).

The spelling of 216581 in words is "two hundred sixteen thousand, five hundred eighty-one".