81689681 has 8 divisors (see below), whose sum is σ = 84476928. Its totient is φ = 78912000.

The previous prime is 81689677. The next prime is 81689711. The reversal of 81689681 is 18698618.

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 81689681 - 2² = 81689677 is a prime.

It is a super-2 number, since 2×81689681² = 13346407963763522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81689581) 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, 17816 + ... + 21926.

It is an arithmetic number, because the mean of its divisors is an integer number (10559616).

Almost surely, 2^81689681 is an apocalyptic number.

It is an amenable number.

81689681 is a deficient number, since it is larger than the sum of its proper divisors (2787247).

81689681 is a wasteful number, since it uses less digits than its factorization.

81689681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4783.

The product of its digits is 165888, while the sum is 47.

The square root of 81689681 is about 9038.2343961639. The cubic root of 81689681 is about 433.8994171123.

The spelling of 81689681 in words is "eighty-one million, six hundred eighty-nine thousand, six hundred eighty-one".