81997 has 4 divisors (see below), whose sum is σ = 82656. Its totient is φ = 81340.

The previous prime is 81973. The next prime is 82003. The reversal of 81997 is 79918.

81997 is nontrivially palindromic in base 6.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 81997 - 2⁷ = 81869 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81937) 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, 79 + ... + 412.

It is an arithmetic number, because the mean of its divisors is an integer number (20664).

2⁸¹⁹⁹⁷ is an apocalyptic number.

It is an amenable number.

81997 is a deficient number, since it is larger than the sum of its proper divisors (659).

81997 is a wasteful number, since it uses less digits than its factorization.

81997 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 658.

The product of its digits is 4536, while the sum is 34.

The square root of 81997 is about 286.3511829904. The cubic root of 81997 is about 43.4442850364. Note that the first 3 decimals are identical.

The spelling of 81997 in words is "eighty-one thousand, nine hundred ninety-seven".