81723139 has 2 divisors, whose sum is σ = 81723140. Its totient is φ = 81723138.

The previous prime is 81723137. The next prime is 81723149. The reversal of 81723139 is 93132718.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81723139 - 2¹ = 81723137 is a prime.

Together with 81723137, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (81723133) 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 as a sum of consecutive naturals, namely, 40861569 + 40861570.

It is an arithmetic number, because the mean of its divisors is an integer number (40861570).

Almost surely, 2^81723139 is an apocalyptic number.

81723139 is a deficient number, since it is larger than the sum of its proper divisors (1).

81723139 is an equidigital number, since it uses as much as digits as its factorization.

81723139 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9072, while the sum is 34.

The square root of 81723139 is about 9040.0851212807. The cubic root of 81723139 is about 433.9586470541.

It can be divided in two parts, 8172 and 3139, that added together give a palindrome (11311).

The spelling of 81723139 in words is "eighty-one million, seven hundred twenty-three thousand, one hundred thirty-nine".