81085729 has 4 divisors (see below), whose sum is σ = 81888660. Its totient is φ = 80282800.

The previous prime is 81085727. The next prime is 81085757. The reversal of 81085729 is 92758018.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 66455104 + 14630625 = 8152^2 + 3825^2 .

It is a cyclic number.

It is not a de Polignac number, because 81085729 - 2¹ = 81085727 is a prime.

It is a super-2 number, since 2×81085729² = 13149790894922882, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 81085691 and 81085700.

It is not an unprimeable number, because it can be changed into a prime (81085721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 401314 + ... + 401515.

It is an arithmetic number, because the mean of its divisors is an integer number (20472165).

Almost surely, 2^81085729 is an apocalyptic number.

It is an amenable number.

81085729 is a deficient number, since it is larger than the sum of its proper divisors (802931).

81085729 is a wasteful number, since it uses less digits than its factorization.

81085729 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 802930.

The product of its (nonzero) digits is 40320, while the sum is 40.

The square root of 81085729 is about 9004.7614626929. The cubic root of 81085729 is about 432.8274624733.

Adding to 81085729 its product of nonzero digits (40320), we get a square (81126049 = 9007²).

The spelling of 81085729 in words is "eighty-one million, eighty-five thousand, seven hundred twenty-nine".