128165115721 has 4 divisors (see below), whose sum is σ = 132584602500. Its totient is φ = 123745628944.

The previous prime is 128165115719. The next prime is 128165115737. The reversal of 128165115721 is 127511561821.

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 56458987321 + 71706128400 = 237611^2 + 267780^2 .

It is a cyclic number.

It is not a de Polignac number, because 128165115721 - 2¹ = 128165115719 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (128165115821) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2209743346 + ... + 2209743403.

It is an arithmetic number, because the mean of its divisors is an integer number (33146150625).

Almost surely, 2^128165115721 is an apocalyptic number.

It is an amenable number.

128165115721 is a deficient number, since it is larger than the sum of its proper divisors (4419486779).

128165115721 is an equidigital number, since it uses as much as digits as its factorization.

128165115721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4419486778.

The product of its digits is 33600, while the sum is 40.

The spelling of 128165115721 in words is "one hundred twenty-eight billion, one hundred sixty-five million, one hundred fifteen thousand, seven hundred twenty-one".