128309561 has 4 divisors (see below), whose sum is σ = 128346192. Its totient is φ = 128272932.

The previous prime is 128309539. The next prime is 128309569. The reversal of 128309561 is 165903821.

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: 165903821 = 107 ⋅1550503.

It is a cyclic number.

It is not a de Polignac number, because 128309561 - 2¹⁴ = 128293177 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (128309569) 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, 12431 + ... + 20276.

It is an arithmetic number, because the mean of its divisors is an integer number (32086548).

Almost surely, 2^128309561 is an apocalyptic number.

It is an amenable number.

128309561 is a deficient number, since it is larger than the sum of its proper divisors (36631).

128309561 is an equidigital number, since it uses as much as digits as its factorization.

128309561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 36630.

The product of its (nonzero) digits is 12960, while the sum is 35.

The square root of 128309561 is about 11327.3810300528. The cubic root of 128309561 is about 504.3743662350.

The spelling of 128309561 in words is "one hundred twenty-eight million, three hundred nine thousand, five hundred sixty-one".