216521231 has 4 divisors (see below), whose sum is σ = 229257792. Its totient is φ = 203784672.

The previous prime is 216521219. The next prime is 216521233. The reversal of 216521231 is 132125612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 216521231 - 2⁶ = 216521167 is a prime.

It is a super-2 number, since 2×216521231² = 93762886947510722, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 216521197 and 216521206.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (216521233) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6368255 + ... + 6368288.

It is an arithmetic number, because the mean of its divisors is an integer number (57314448).

Almost surely, 2^216521231 is an apocalyptic number.

216521231 is a deficient number, since it is larger than the sum of its proper divisors (12736561).

216521231 is a wasteful number, since it uses less digits than its factorization.

216521231 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12736560.

The product of its digits is 720, while the sum is 23.

The square root of 216521231 is about 14714.6604106245. The cubic root of 216521231 is about 600.4822336104.

Adding to 216521231 its reverse (132125612), we get a palindrome (348646843).

The spelling of 216521231 in words is "two hundred sixteen million, five hundred twenty-one thousand, two hundred thirty-one".