81728797 has 4 divisors (see below), whose sum is σ = 81787420. Its totient is φ = 81670176.

The previous prime is 81728791. The next prime is 81728807. The reversal of 81728797 is 79782718.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 79782718 = 2 ⋅39891359.

It can be written as a sum of positive squares in 2 ways, for example, as 40627876 + 41100921 = 6374^2 + 6411^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81728797 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 81728797.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81728791) 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, 27168 + ... + 30025.

It is an arithmetic number, because the mean of its divisors is an integer number (20446855).

Almost surely, 2^81728797 is an apocalyptic number.

It is an amenable number.

81728797 is a deficient number, since it is larger than the sum of its proper divisors (58623).

81728797 is a wasteful number, since it uses less digits than its factorization.

81728797 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 58622.

The product of its digits is 395136, while the sum is 49.

The square root of 81728797 is about 9040.3980553956. The cubic root of 81728797 is about 433.9686616856.

The spelling of 81728797 in words is "eighty-one million, seven hundred twenty-eight thousand, seven hundred ninety-seven".