81239831 has 4 divisors (see below), whose sum is σ = 82772712. Its totient is φ = 79706952.

The previous prime is 81239813. The next prime is 81239843. The reversal of 81239831 is 13893218.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81239831 is a prime.

It is a super-2 number, since 2×81239831² = 13199820281817122, 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 = 81239791 and 81239800.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81239891) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 766361 + ... + 766466.

It is an arithmetic number, because the mean of its divisors is an integer number (20693178).

Almost surely, 2^81239831 is an apocalyptic number.

81239831 is a deficient number, since it is larger than the sum of its proper divisors (1532881).

81239831 is a wasteful number, since it uses less digits than its factorization.

81239831 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1532880.

The product of its digits is 10368, while the sum is 35.

The square root of 81239831 is about 9013.3140963799. The cubic root of 81239831 is about 433.1014826131.

The spelling of 81239831 in words is "eighty-one million, two hundred thirty-nine thousand, eight hundred thirty-one".