81879919 has 4 divisors (see below), whose sum is σ = 89323560. Its totient is φ = 74436280.

The previous prime is 81879893. The next prime is 81879961. The reversal of 81879919 is 91997818.

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 81879919 - 2⁵ = 81879887 is a prime.

It is a super-2 number, since 2×81879919² = 13408642270893122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81879979) 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, 3721804 + ... + 3721825.

It is an arithmetic number, because the mean of its divisors is an integer number (22330890).

Almost surely, 2^81879919 is an apocalyptic number.

81879919 is a deficient number, since it is larger than the sum of its proper divisors (7443641).

81879919 is a wasteful number, since it uses less digits than its factorization.

81879919 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7443640.

The product of its digits is 326592, while the sum is 52.

The square root of 81879919 is about 9048.7523449368. The cubic root of 81879919 is about 434.2359759983.

It can be divided in two parts, 818799 and 19, that added together give a palindrome (818818).

The spelling of 81879919 in words is "eighty-one million, eight hundred seventy-nine thousand, nine hundred nineteen".