128565990721 has 27 divisors (see below), whose sum is σ = 150920481123. Its totient is φ = 109203338160.

The previous prime is 128565990719. The next prime is 128565990731. The reversal of 128565990721 is 127099565821.

The square root of 128565990721 is 358561.

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

It can be written as a sum of positive squares in only one way, i.e., 1416694321 + 127149296400 = 37639^2 + 356580^2 .

It is not a de Polignac number, because 128565990721 - 2¹ = 128565990719 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (128565990731) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 454296646 + ... + 454296928.

It is an arithmetic number, because the mean of its divisors is an integer number (5589647449).

Almost surely, 2^128565990721 is an apocalyptic number.

128565990721 is the 358561-st square number.

128565990721 is the 179281-st centered octagonal number.

It is an amenable number.

128565990721 is a deficient number, since it is larger than the sum of its proper divisors (22354490402).

128565990721 is an frugal number, since it uses more digits than its factorization.

128565990721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 942 (or 471 counting only the distinct ones).

The product of its (nonzero) digits is 2721600, while the sum is 55.

The spelling of 128565990721 in words is "one hundred twenty-eight billion, five hundred sixty-five million, nine hundred ninety thousand, seven hundred twenty-one".