216111221 has 4 divisors (see below), whose sum is σ = 216203052. Its totient is φ = 216019392.

The previous prime is 216111211. The next prime is 216111229. The reversal of 216111221 is 122111612.

216111221 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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

It can be written as a sum of positive squares in 2 ways, for example, as 166126321 + 49984900 = 12889^2 + 7070^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-216111221 is a prime.

It is a super-2 number, since 2×216111221² = 93408119684221682, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 216111221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (216111229) 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, 42290 + ... + 47123.

It is an arithmetic number, because the mean of its divisors is an integer number (54050763).

Almost surely, 2^216111221 is an apocalyptic number.

It is an amenable number.

216111221 is a deficient number, since it is larger than the sum of its proper divisors (91831).

216111221 is an equidigital number, since it uses as much as digits as its factorization.

216111221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 91830.

The product of its digits is 48, while the sum is 17.

The square root of 216111221 is about 14700.7217850009. The cubic root of 216111221 is about 600.1029647368.

Adding to 216111221 its reverse (122111612), we get a palindrome (338222833).

The spelling of 216111221 in words is "two hundred sixteen million, one hundred eleven thousand, two hundred twenty-one".