128817221 has 4 divisors (see below), whose sum is σ = 138726252. Its totient is φ = 118908192.

The previous prime is 128817209. The next prime is 128817223. The reversal of 128817221 is 122718821.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 122718821 = 10687 ⋅11483.

It can be written as a sum of positive squares in 2 ways, for example, as 80013025 + 48804196 = 8945^2 + 6986^2 .

It is not a de Polignac number, because 128817221 - 2²⁶ = 61708357 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 (128817223) 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, 4954496 + ... + 4954521.

It is an arithmetic number, because the mean of its divisors is an integer number (34681563).

Almost surely, 2^128817221 is an apocalyptic number.

It is an amenable number.

128817221 is a deficient number, since it is larger than the sum of its proper divisors (9909031).

128817221 is an equidigital number, since it uses as much as digits as its factorization.

128817221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9909030.

The product of its digits is 3584, while the sum is 32.

The square root of 128817221 is about 11349.7674425514. The cubic root of 128817221 is about 505.0386808263.

It can be divided in two parts, 12881 and 7221, that added together give a palindrome (20102).

The spelling of 128817221 in words is "one hundred twenty-eight million, eight hundred seventeen thousand, two hundred twenty-one".