128321561 has 4 divisors (see below), whose sum is σ = 128350992. Its totient is φ = 128292132.

The previous prime is 128321551. The next prime is 128321597. The reversal of 128321561 is 165123821.

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, and also an emirpimes, since its reverse is a distinct semiprime: 165123821 = 619 ⋅266759.

It is a cyclic number.

It is not a de Polignac number, because 128321561 - 2¹⁰ = 128320537 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (128321551) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6731 + ... + 17376.

It is an arithmetic number, because the mean of its divisors is an integer number (32087748).

Almost surely, 2^128321561 is an apocalyptic number.

It is an amenable number.

128321561 is a deficient number, since it is larger than the sum of its proper divisors (29431).

128321561 is an equidigital number, since it uses as much as digits as its factorization.

128321561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 29430.

The product of its digits is 2880, while the sum is 29.

The square root of 128321561 is about 11327.9107076283. The cubic root of 128321561 is about 504.3900894169.

The spelling of 128321561 in words is "one hundred twenty-eight million, three hundred twenty-one thousand, five hundred sixty-one".