216711221 has 4 divisors (see below), whose sum is σ = 226133472. Its totient is φ = 207288972.

The previous prime is 216711217. The next prime is 216711233. The reversal of 216711221 is 122117612.

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 not a de Polignac number, because 216711221 - 2² = 216711217 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (23), and also a Moran number because the ratio is a prime number: 9422227 = 216711221 / (2 + 1 + 6 + 7 + 1 + 1 + 2 + 2 + 1).

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (216711251) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4711091 + ... + 4711136.

It is an arithmetic number, because the mean of its divisors is an integer number (56533368).

Almost surely, 2^216711221 is an apocalyptic number.

It is an amenable number.

216711221 is a deficient number, since it is larger than the sum of its proper divisors (9422251).

216711221 is an equidigital number, since it uses as much as digits as its factorization.

216711221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9422250.

The product of its digits is 336, while the sum is 23.

The square root of 216711221 is about 14721.1148015359. The cubic root of 216711221 is about 600.6578164952.

Adding to 216711221 its reverse (122117612), we get a palindrome (338828833).

The spelling of 216711221 in words is "two hundred sixteen million, seven hundred eleven thousand, two hundred twenty-one".