81919979 has 4 divisors (see below), whose sum is σ = 82097376. Its totient is φ = 81742584.

The previous prime is 81919973. The next prime is 81919993. The reversal of 81919979 is 97991918.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 97991918 = 2 ⋅48995959.

It is a cyclic number.

It is not a de Polignac number, because 81919979 - 2²⁰ = 80871403 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81919979.

It is not an unprimeable number, because it can be changed into a prime (81919973) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 88004 + ... + 88929.

It is an arithmetic number, because the mean of its divisors is an integer number (20524344).

Almost surely, 2^81919979 is an apocalyptic number.

81919979 is a deficient number, since it is larger than the sum of its proper divisors (177397).

81919979 is a wasteful number, since it uses less digits than its factorization.

81919979 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 177396.

The product of its digits is 367416, while the sum is 53.

The square root of 81919979 is about 9050.9656390907. The cubic root of 81919979 is about 434.3067815440.

The spelling of 81919979 in words is "eighty-one million, nine hundred nineteen thousand, nine hundred seventy-nine".