128509661 has 4 divisors (see below), whose sum is σ = 146868192. Its totient is φ = 110151132.

The previous prime is 128509657. The next prime is 128509691. The reversal of 128509661 is 166905821.

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.

It is not a de Polignac number, because 128509661 - 2² = 128509657 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (128509631) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9179255 + ... + 9179268.

It is an arithmetic number, because the mean of its divisors is an integer number (36717048).

Almost surely, 2^128509661 is an apocalyptic number.

It is an amenable number.

128509661 is a deficient number, since it is larger than the sum of its proper divisors (18358531).

128509661 is an equidigital number, since it uses as much as digits as its factorization.

128509661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18358530.

The product of its (nonzero) digits is 25920, while the sum is 38.

The square root of 128509661 is about 11336.2101691879. The cubic root of 128509661 is about 504.6364222881.

The spelling of 128509661 in words is "one hundred twenty-eight million, five hundred nine thousand, six hundred sixty-one".