128531 has 4 divisors (see below), whose sum is σ = 138432. Its totient is φ = 118632.

The previous prime is 128521. The next prime is 128549. The reversal of 128531 is 135821.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 135821 = 7 ⋅19403.

It is a cyclic number.

It is not a de Polignac number, because 128531 - 2⁶ = 128467 is a prime.

It is a super-2 number, since 2×128531² = 33040435922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (128521) 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, 4931 + ... + 4956.

It is an arithmetic number, because the mean of its divisors is an integer number (34608).

2¹²⁸⁵³¹ is an apocalyptic number.

128531 is a deficient number, since it is larger than the sum of its proper divisors (9901).

128531 is an equidigital number, since it uses as much as digits as its factorization.

128531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9900.

The product of its digits is 240, while the sum is 20.

The square root of 128531 is about 358.5122034185. The cubic root of 128531 is about 50.4664352330.

The spelling of 128531 in words is "one hundred twenty-eight thousand, five hundred thirty-one".