128009639 has 4 divisors (see below), whose sum is σ = 129329424. Its totient is φ = 126689856.

The previous prime is 128009627. The next prime is 128009657. The reversal of 128009639 is 936900821.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 128009639 - 2⁸ = 128009383 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 (128009689) 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, 659747 + ... + 659940.

It is an arithmetic number, because the mean of its divisors is an integer number (32332356).

Almost surely, 2^128009639 is an apocalyptic number.

128009639 is a deficient number, since it is larger than the sum of its proper divisors (1319785).

128009639 is an equidigital number, since it uses as much as digits as its factorization.

128009639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1319784.

The product of its (nonzero) digits is 23328, while the sum is 38.

The square root of 128009639 is about 11314.1344786068. The cubic root of 128009639 is about 503.9810700352.

The spelling of 128009639 in words is "one hundred twenty-eight million, nine thousand, six hundred thirty-nine".