81665917 has 4 divisors (see below), whose sum is σ = 81774556. Its totient is φ = 81557280.

The previous prime is 81665897. The next prime is 81665923. The reversal of 81665917 is 71956618.

It is a happy number.

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

It can be written as a sum of positive squares in 2 ways, for example, as 34798201 + 46867716 = 5899^2 + 6846^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81665917 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 (81665957) 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, 53184 + ... + 54697.

It is an arithmetic number, because the mean of its divisors is an integer number (20443639).

Almost surely, 2^81665917 is an apocalyptic number.

It is an amenable number.

81665917 is a deficient number, since it is larger than the sum of its proper divisors (108639).

81665917 is a wasteful number, since it uses less digits than its factorization.

81665917 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 108638.

The product of its digits is 90720, while the sum is 43.

The square root of 81665917 is about 9036.9196632481. The cubic root of 81665917 is about 433.8573384162.

The spelling of 81665917 in words is "eighty-one million, six hundred sixty-five thousand, nine hundred seventeen".