81728819 has 4 divisors (see below), whose sum is σ = 83937744. Its totient is φ = 79519896.

The previous prime is 81728813. The next prime is 81728839. The reversal of 81728819 is 91882718.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 91882718 = 2 ⋅45941359.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81728819 is a prime.

It is a super-2 number, since 2×81728819² = 13359199710269522, which contains 22 as substring.

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 81728819.

It is not an unprimeable number, because it can be changed into a prime (81728813) 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, 1104407 + ... + 1104480.

It is an arithmetic number, because the mean of its divisors is an integer number (20984436).

Almost surely, 2^81728819 is an apocalyptic number.

81728819 is a deficient number, since it is larger than the sum of its proper divisors (2208925).

81728819 is a wasteful number, since it uses less digits than its factorization.

81728819 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2208924.

The product of its digits is 64512, while the sum is 44.

The square root of 81728819 is about 9040.3992721561. The cubic root of 81728819 is about 433.9687006246.

The spelling of 81728819 in words is "eighty-one million, seven hundred twenty-eight thousand, eight hundred nineteen".