81591079 has 4 divisors (see below), whose sum is σ = 81650800. Its totient is φ = 81531360.

The previous prime is 81591071. The next prime is 81591113. The reversal of 81591079 is 97019518.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 97019518 = 2 ⋅48509759.

It is a cyclic number.

It is not a de Polignac number, because 81591079 - 2³ = 81591071 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81591071) 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, 27762 + ... + 30559.

It is an arithmetic number, because the mean of its divisors is an integer number (20412700).

Almost surely, 2^81591079 is an apocalyptic number.

81591079 is a deficient number, since it is larger than the sum of its proper divisors (59721).

81591079 is a wasteful number, since it uses less digits than its factorization.

81591079 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 59720.

The product of its (nonzero) digits is 22680, while the sum is 40.

The square root of 81591079 is about 9032.7780333627. The cubic root of 81591079 is about 433.7247701027.

The spelling of 81591079 in words is "eighty-one million, five hundred ninety-one thousand, seventy-nine".