81739681 has 3 divisors (see below), whose sum is σ = 81748723. Its totient is φ = 81730640.

The previous prime is 81739663. The next prime is 81739699. The reversal of 81739681 is 18693718.

The square root of 81739681 is 9041.

It is a perfect power (a square), and thus also a powerful number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is an interprime number because it is at equal distance from previous prime (81739663) and next prime (81739699).

It can be written as a sum of positive squares in only one way, i.e., 81162081 + 577600 = 9009^2 + 760^2 .

It is not a de Polignac number, because 81739681 - 2¹¹ = 81737633 is a prime.

It is a super-2 number, since 2×81739681² = 13362750899963522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81739601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 4521 + ... + 13561.

Almost surely, 2^81739681 is an apocalyptic number.

81739681 is the 9041-st square number.

81739681 is the 4521-st centered octagonal number.

It is an amenable number.

81739681 is a deficient number, since it is larger than the sum of its proper divisors (9042).

81739681 is an frugal number, since it uses more digits than its factorization.

81739681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18082 (or 9041 counting only the distinct ones).

The product of its digits is 72576, while the sum is 43.

The cubic root of 81739681 is about 433.9879250111.

The spelling of 81739681 in words is "eighty-one million, seven hundred thirty-nine thousand, six hundred eighty-one".