81731665 has 8 divisors (see below), whose sum is σ = 103847400. Its totient is φ = 61539072.

The previous prime is 81731651. The next prime is 81731669. The reversal of 81731665 is 56613718.

It can be written as a sum of positive squares in 4 ways, for example, as 26956864 + 54774801 = 5192^2 + 7401^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 81731665 - 2¹⁹ = 81207377 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81731669) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 480690 + ... + 480859.

It is an arithmetic number, because the mean of its divisors is an integer number (12980925).

Almost surely, 2^81731665 is an apocalyptic number.

81731665 is a gapful number since it is divisible by the number (85) formed by its first and last digit.

It is an amenable number.

81731665 is a deficient number, since it is larger than the sum of its proper divisors (22115735).

81731665 is a wasteful number, since it uses less digits than its factorization.

81731665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 961571.

The product of its digits is 30240, while the sum is 37.

The square root of 81731665 is about 9040.5566753381. The cubic root of 81731665 is about 433.9737378546.

The spelling of 81731665 in words is "eighty-one million, seven hundred thirty-one thousand, six hundred sixty-five".