81549729 has 24 divisors (see below), whose sum is σ = 125180640. Its totient is φ = 51012288.

The previous prime is 81549703. The next prime is 81549733. The reversal of 81549729 is 92794518.

81549729 is a `hidden beast` number, since 81 + 549 + 7 + 29 = 666.

It is not a de Polignac number, because 81549729 - 2⁸ = 81549473 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81549749) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 16069 + ... + 20525.

It is an arithmetic number, because the mean of its divisors is an integer number (5215860).

Almost surely, 2^81549729 is an apocalyptic number.

It is an amenable number.

81549729 is a deficient number, since it is larger than the sum of its proper divisors (43630911).

81549729 is a wasteful number, since it uses less digits than its factorization.

81549729 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4589 (or 4586 counting only the distinct ones).

The product of its digits is 181440, while the sum is 45.

The square root of 81549729 is about 9030.4888571993. The cubic root of 81549729 is about 433.6514877863.

The spelling of 81549729 in words is "eighty-one million, five hundred forty-nine thousand, seven hundred twenty-nine".