81728669 has 4 divisors (see below), whose sum is σ = 89158560. Its totient is φ = 74298780.

The previous prime is 81728659. The next prime is 81728693. The reversal of 81728669 is 96682718.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 81728669 - 2⁴ = 81728653 is a prime.

It is a super-2 number, since 2×81728669² = 13359150673023122, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81728609) 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, 3714929 + ... + 3714950.

It is an arithmetic number, because the mean of its divisors is an integer number (22289640).

Almost surely, 2^81728669 is an apocalyptic number.

It is an amenable number.

81728669 is a deficient number, since it is larger than the sum of its proper divisors (7429891).

81728669 is a wasteful number, since it uses less digits than its factorization.

81728669 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7429890.

The product of its digits is 290304, while the sum is 47.

The square root of 81728669 is about 9040.3909760585. The cubic root of 81728669 is about 433.9684351313.

The spelling of 81728669 in words is "eighty-one million, seven hundred twenty-eight thousand, six hundred sixty-nine".