12789121921 has 3 divisors (see below), whose sum is σ = 12789235011. Its totient is φ = 12789008832.

The previous prime is 12789121909. The next prime is 12789121931. The reversal of 12789121921 is 12912198721.

It is a happy number.

The square root of 12789121921 is 113089.

It is a perfect power (a square), and thus also a powerful number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 12912198721 = 12251 ⋅1053971.

It can be written as a sum of positive squares in only one way, i.e., 5873536321 + 6915585600 = 76639^2 + 83160^2 .

It is not a de Polignac number, because 12789121921 - 2²³ = 12780733313 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (12789121931) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 56545 + ... + 169633.

It is an arithmetic number, because the mean of its divisors is an integer number (4263078337).

Almost surely, 2^12789121921 is an apocalyptic number.

12789121921 is the 113089-th square number.

12789121921 is the 56545-th centered octagonal number.

It is an amenable number.

12789121921 is a deficient number, since it is larger than the sum of its proper divisors (113090).

12789121921 is an frugal number, since it uses more digits than its factorization.

12789121921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 226178 (or 113089 counting only the distinct ones).

The product of its digits is 36288, while the sum is 43.

The spelling of 12789121921 in words is "twelve billion, seven hundred eighty-nine million, one hundred twenty-one thousand, nine hundred twenty-one".