81331531 has 4 divisors (see below), whose sum is σ = 81549952. Its totient is φ = 81113112.

The previous prime is 81331489. The next prime is 81331561. The reversal of 81331531 is 13513318.

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

It is a cyclic number.

It is not a de Polignac number, because 81331531 - 2⁷ = 81331403 is a prime.

It is a super-2 number, since 2×81331531² = 13229635869607922, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 81331496 and 81331505.

It is not an unprimeable number, because it can be changed into a prime (81331561) 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, 108651 + ... + 109396.

It is an arithmetic number, because the mean of its divisors is an integer number (20387488).

Almost surely, 2^81331531 is an apocalyptic number.

81331531 is a deficient number, since it is larger than the sum of its proper divisors (218421).

81331531 is a wasteful number, since it uses less digits than its factorization.

81331531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 218420.

The product of its digits is 1080, while the sum is 25.

The square root of 81331531 is about 9018.3995808569. The cubic root of 81331531 is about 433.2643767329.

Adding to 81331531 its reverse (13513318), we get a palindrome (94844849).

The spelling of 81331531 in words is "eighty-one million, three hundred thirty-one thousand, five hundred thirty-one".