217908121 has 4 divisors (see below), whose sum is σ = 222544512. Its totient is φ = 213271732.

The previous prime is 217908109. The next prime is 217908127. The reversal of 217908121 is 121809712.

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 a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-217908121 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (217908127) 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, 2318125 + ... + 2318218.

It is an arithmetic number, because the mean of its divisors is an integer number (55636128).

Almost surely, 2^217908121 is an apocalyptic number.

It is an amenable number.

217908121 is a deficient number, since it is larger than the sum of its proper divisors (4636391).

217908121 is an equidigital number, since it uses as much as digits as its factorization.

217908121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4636390.

The product of its (nonzero) digits is 2016, while the sum is 31.

The square root of 217908121 is about 14761.7113167817. The cubic root of 217908121 is about 601.7616015751.

The spelling of 217908121 in words is "two hundred seventeen million, nine hundred eight thousand, one hundred twenty-one".