81731685 has 16 divisors (see below), whose sum is σ = 149452416. Its totient is φ = 37363008.

The previous prime is 81731681. The next prime is 81731687. The reversal of 81731685 is 58613718.

It is not a de Polignac number, because 81731685 - 2² = 81731681 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81731681) 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 15 ways as a sum of consecutive naturals, for example, 389094 + ... + 389303.

It is an arithmetic number, because the mean of its divisors is an integer number (9340776).

Almost surely, 2^81731685 is an apocalyptic number.

It is an amenable number.

81731685 is a deficient number, since it is larger than the sum of its proper divisors (67720731).

81731685 is a wasteful number, since it uses less digits than its factorization.

81731685 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 778412.

The product of its digits is 40320, while the sum is 39.

The square root of 81731685 is about 9040.5577814646. The cubic root of 81731685 is about 433.9737732529.

The spelling of 81731685 in words is "eighty-one million, seven hundred thirty-one thousand, six hundred eighty-five".