81373681 has 4 divisors (see below), whose sum is σ = 84179700. Its totient is φ = 78567664.

The previous prime is 81373657. The next prime is 81373697. The reversal of 81373681 is 18637318.

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 46799281 + 34574400 = 6841^2 + 5880^2 .

It is a cyclic number.

It is not a de Polignac number, because 81373681 - 2⁷ = 81373553 is a prime.

It is a super-2 number, since 2×81373681² = 13243351918979522, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81373681.

It is not an unprimeable number, because it can be changed into a prime (81373601) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1402966 + ... + 1403023.

It is an arithmetic number, because the mean of its divisors is an integer number (21044925).

Almost surely, 2^81373681 is an apocalyptic number.

It is an amenable number.

81373681 is a deficient number, since it is larger than the sum of its proper divisors (2806019).

81373681 is a wasteful number, since it uses less digits than its factorization.

81373681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2806018.

The product of its digits is 24192, while the sum is 37.

The square root of 81373681 is about 9020.7361672981. The cubic root of 81373681 is about 433.3392101110.

The spelling of 81373681 in words is "eighty-one million, three hundred seventy-three thousand, six hundred eighty-one".