217992121 has 4 divisors (see below), whose sum is σ = 223309044. Its totient is φ = 212675200.

The previous prime is 217992119. The next prime is 217992133. The reversal of 217992121 is 121299712.

It is a happy number.

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 27248400 + 190743721 = 5220^2 + 13811^2 .

It is not a de Polignac number, because 217992121 - 2¹ = 217992119 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (217992161) 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, 2658400 + ... + 2658481.

It is an arithmetic number, because the mean of its divisors is an integer number (55827261).

Almost surely, 2^217992121 is an apocalyptic number.

It is an amenable number.

217992121 is a deficient number, since it is larger than the sum of its proper divisors (5316923).

217992121 is an equidigital number, since it uses as much as digits as its factorization.

217992121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5316922.

The product of its digits is 4536, while the sum is 34.

The square root of 217992121 is about 14764.5562412150. The cubic root of 217992121 is about 601.8389147114.

The spelling of 217992121 in words is "two hundred seventeen million, nine hundred ninety-two thousand, one hundred twenty-one".