81728557 has 8 divisors (see below), whose sum is σ = 86165600. Its totient is φ = 77305104.

The previous prime is 81728531. The next prime is 81728561. The reversal of 81728557 is 75582718.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 81728557 - 2¹⁹ = 81204269 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 (81728567) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10438 + ... + 16504.

It is an arithmetic number, because the mean of its divisors is an integer number (10770700).

Almost surely, 2^81728557 is an apocalyptic number.

It is an amenable number.

81728557 is a deficient number, since it is larger than the sum of its proper divisors (4437043).

81728557 is a wasteful number, since it uses less digits than its factorization.

81728557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6795.

The product of its digits is 156800, while the sum is 43.

The square root of 81728557 is about 9040.3847816340. The cubic root of 81728557 is about 433.9682368962.

The spelling of 81728557 in words is "eighty-one million, seven hundred twenty-eight thousand, five hundred fifty-seven".