128399021 has 2 divisors, whose sum is σ = 128399022. Its totient is φ = 128399020.

The previous prime is 128398981. The next prime is 128399023. The reversal of 128399021 is 120993821.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 119464900 + 8934121 = 10930^2 + 2989^2 .

It is a cyclic number.

It is not a de Polignac number, because 128399021 - 2²⁶ = 61290157 is a prime.

It is a Sophie Germain prime.

Together with 128399023, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (128399023) 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 as a sum of consecutive naturals, namely, 64199510 + 64199511.

It is an arithmetic number, because the mean of its divisors is an integer number (64199511).

Almost surely, 2^128399021 is an apocalyptic number.

It is an amenable number.

128399021 is a deficient number, since it is larger than the sum of its proper divisors (1).

128399021 is an equidigital number, since it uses as much as digits as its factorization.

128399021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 7776, while the sum is 35.

The square root of 128399021 is about 11331.3291806390. The cubic root of 128399021 is about 504.4915589783.

The spelling of 128399021 in words is "one hundred twenty-eight million, three hundred ninety-nine thousand, twenty-one".