128921813 has 4 divisors (see below), whose sum is σ = 130062828. Its totient is φ = 127780800.

The previous prime is 128921809. The next prime is 128921851. The reversal of 128921813 is 318129821.

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 26142769 + 102779044 = 5113^2 + 10138^2 .

It is a cyclic number.

It is not a de Polignac number, because 128921813 - 2² = 128921809 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (128921873) 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, 570338 + ... + 570563.

It is an arithmetic number, because the mean of its divisors is an integer number (32515707).

Almost surely, 2^128921813 is an apocalyptic number.

It is an amenable number.

128921813 is a deficient number, since it is larger than the sum of its proper divisors (1141015).

128921813 is a wasteful number, since it uses less digits than its factorization.

128921813 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1141014.

The product of its digits is 6912, while the sum is 35.

The square root of 128921813 is about 11354.3741791435. The cubic root of 128921813 is about 505.1753310748.

The spelling of 128921813 in words is "one hundred twenty-eight million, nine hundred twenty-one thousand, eight hundred thirteen".