128128981 has 4 divisors (see below), whose sum is σ = 128198700. Its totient is φ = 128059264.

The previous prime is 128128963. The next prime is 128128999. The reversal of 128128981 is 189821821.

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

It is an interprime number because it is at equal distance from previous prime (128128963) and next prime (128128999).

It can be written as a sum of positive squares in 2 ways, for example, as 76720081 + 51408900 = 8759^2 + 7170^2 .

It is a cyclic number.

It is not a de Polignac number, because 128128981 - 2²⁵ = 94574549 is a prime.

It is a super-2 number, since 2×128128981² = 32834071544196722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (128128961) 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, 32026 + ... + 35803.

It is an arithmetic number, because the mean of its divisors is an integer number (32049675).

Almost surely, 2^128128981 is an apocalyptic number.

It is an amenable number.

128128981 is a deficient number, since it is larger than the sum of its proper divisors (69719).

128128981 is an equidigital number, since it uses as much as digits as its factorization.

128128981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 69718.

The product of its digits is 18432, while the sum is 40.

The square root of 128128981 is about 11319.4072724679. The cubic root of 128128981 is about 504.1376400868.

The spelling of 128128981 in words is "one hundred twenty-eight million, one hundred twenty-eight thousand, nine hundred eighty-one".