128909821 has 4 divisors (see below), whose sum is σ = 128947132. Its totient is φ = 128872512.

The previous prime is 128909819. The next prime is 128909839.

128909821 is nontrivially palindromic in base 10.

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

It can be written as a sum of positive squares in 2 ways, for example, as 98505625 + 30404196 = 9925^2 + 5514^2 .

It is a cyclic number.

It is not a de Polignac number, because 128909821 - 2¹ = 128909819 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 (128909881) 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, 12876 + ... + 20581.

It is an arithmetic number, because the mean of its divisors is an integer number (32236783).

Almost surely, 2^128909821 is an apocalyptic number.

It is an amenable number.

128909821 is a deficient number, since it is larger than the sum of its proper divisors (37311).

128909821 is an equidigital number, since it uses as much as digits as its factorization.

128909821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 37310.

The product of its (nonzero) digits is 20736, while the sum is 40.

The square root of 128909821 is about 11353.8460884407. The cubic root of 128909821 is about 505.1596671870.

The spelling of 128909821 in words is "one hundred twenty-eight million, nine hundred nine thousand, eight hundred twenty-one".