81731693 has 4 divisors (see below), whose sum is σ = 81848988. Its totient is φ = 81614400.

The previous prime is 81731687. The next prime is 81731701. The reversal of 81731693 is 39613718.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 39613718 = 2 ⋅19806859.

It can be written as a sum of positive squares in 2 ways, for example, as 44983849 + 36747844 = 6707^2 + 6062^2 .

It is a cyclic number.

It is not a de Polignac number, because 81731693 - 2¹⁶ = 81666157 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81737693) 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, 57596 + ... + 58997.

It is an arithmetic number, because the mean of its divisors is an integer number (20462247).

Almost surely, 2^81731693 is an apocalyptic number.

It is an amenable number.

81731693 is a deficient number, since it is larger than the sum of its proper divisors (117295).

81731693 is a wasteful number, since it uses less digits than its factorization.

81731693 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 117294.

The product of its digits is 27216, while the sum is 38.

The square root of 81731693 is about 9040.5582239152. The cubic root of 81731693 is about 433.9737874122.

The spelling of 81731693 in words is "eighty-one million, seven hundred thirty-one thousand, six hundred ninety-three".