217865221 has 12 divisors (see below), whose sum is σ = 257593260. Its totient is φ = 183677760.

The previous prime is 217865203. The next prime is 217865227. The reversal of 217865221 is 122568712.

It is a happy number.

217865221 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 2 ways, for example, as 96314596 + 121550625 = 9814^2 + 11025^2 .

It is not a de Polignac number, because 217865221 - 2⁵ = 217865189 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (217865227) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 33456 + ... + 39433.

It is an arithmetic number, because the mean of its divisors is an integer number (21466105).

Almost surely, 2^217865221 is an apocalyptic number.

It is an amenable number.

217865221 is a deficient number, since it is larger than the sum of its proper divisors (39728039).

217865221 is an equidigital number, since it uses as much as digits as its factorization.

217865221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 72964 (or 72957 counting only the distinct ones).

The product of its digits is 13440, while the sum is 34.

The square root of 217865221 is about 14760.2581616989. The cubic root of 217865221 is about 601.7221089870.

The spelling of 217865221 in words is "two hundred seventeen million, eight hundred sixty-five thousand, two hundred twenty-one".