81908731 has 4 divisors (see below), whose sum is σ = 84733200. Its totient is φ = 79084264.

The previous prime is 81908719. The next prime is 81908759. The reversal of 81908731 is 13780918.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81908731 - 2⁵ = 81908699 is a prime.

It is a super-2 number, since 2×81908731² = 13418080428060722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81902731) 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 3 ways as a sum of consecutive naturals, for example, 1412191 + ... + 1412248.

It is an arithmetic number, because the mean of its divisors is an integer number (21183300).

Almost surely, 2^81908731 is an apocalyptic number.

81908731 is a deficient number, since it is larger than the sum of its proper divisors (2824469).

81908731 is a wasteful number, since it uses less digits than its factorization.

81908731 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2824468.

The product of its (nonzero) digits is 12096, while the sum is 37.

The square root of 81908731 is about 9050.3442475963. The cubic root of 81908731 is about 434.2869031768.

The spelling of 81908731 in words is "eighty-one million, nine hundred eight thousand, seven hundred thirty-one".