128138921 has 4 divisors (see below), whose sum is σ = 128162244. Its totient is φ = 128115600.

The previous prime is 128138893. The next prime is 128138929. The reversal of 128138921 is 129831821.

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 71588521 + 56550400 = 8461^2 + 7520^2 .

It is a cyclic number.

It is not a de Polignac number, because 128138921 - 2¹⁰ = 128137897 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (128138929) 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, 1631 + ... + 16091.

It is an arithmetic number, because the mean of its divisors is an integer number (32040561).

Almost surely, 2^128138921 is an apocalyptic number.

It is an amenable number.

128138921 is a deficient number, since it is larger than the sum of its proper divisors (23323).

128138921 is an equidigital number, since it uses as much as digits as its factorization.

128138921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23322.

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

The square root of 128138921 is about 11319.8463328793. The cubic root of 128138921 is about 504.1506764260.

The spelling of 128138921 in words is "one hundred twenty-eight million, one hundred thirty-eight thousand, nine hundred twenty-one".