81331985 has 16 divisors (see below), whose sum is σ = 112569600. Its totient is φ = 55256256.

The previous prime is 81331981. The next prime is 81331997. The reversal of 81331985 is 58913318.

It is a cyclic number.

It is not a de Polignac number, because 81331985 - 2² = 81331981 is a prime.

It is a super-2 number, since 2×81331985² = 13229783568080450, which contains 22 as substring.

It is a Smith number, since the sum of its digits (38) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81331981) 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 15 ways as a sum of consecutive naturals, for example, 6845 + ... + 14474.

It is an arithmetic number, because the mean of its divisors is an integer number (7035600).

Almost surely, 2^81331985 is an apocalyptic number.

It is an amenable number.

81331985 is a deficient number, since it is larger than the sum of its proper divisors (31237615).

81331985 is a wasteful number, since it uses less digits than its factorization.

81331985 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21440.

The product of its digits is 25920, while the sum is 38.

The square root of 81331985 is about 9018.4247515849. The cubic root of 81331985 is about 433.2651829051.

The spelling of 81331985 in words is "eighty-one million, three hundred thirty-one thousand, nine hundred eighty-five".