128821021 has 4 divisors (see below), whose sum is σ = 147224032. Its totient is φ = 110418012.

The previous prime is 128821001. The next prime is 128821039. The reversal of 128821021 is 120128821.

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 a cyclic number.

It is not a de Polignac number, because 128821021 - 2¹⁹ = 128296733 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 (128821001) 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, 9201495 + ... + 9201508.

It is an arithmetic number, because the mean of its divisors is an integer number (36806008).

Almost surely, 2^128821021 is an apocalyptic number.

It is an amenable number.

128821021 is a deficient number, since it is larger than the sum of its proper divisors (18403011).

128821021 is an equidigital number, since it uses as much as digits as its factorization.

128821021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18403010.

The product of its (nonzero) digits is 512, while the sum is 25.

The square root of 128821021 is about 11349.9348456280. The cubic root of 128821021 is about 505.0436468500.

Adding to 128821021 its reverse (120128821), we get a palindrome (248949842).

The spelling of 128821021 in words is "one hundred twenty-eight million, eight hundred twenty-one thousand, twenty-one".