81966565 has 4 divisors (see below), whose sum is σ = 98359884. Its totient is φ = 65573248.

The previous prime is 81966559. The next prime is 81966611. The reversal of 81966565 is 56566918.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 56566918 = 2 ⋅28283459.

It can be written as a sum of positive squares in 2 ways, for example, as 13557124 + 68409441 = 3682^2 + 8271^2 .

It is a cyclic number.

It is not a de Polignac number, because 81966565 - 2²³ = 73577957 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8196652 + ... + 8196661.

It is an arithmetic number, because the mean of its divisors is an integer number (24589971).

Almost surely, 2^81966565 is an apocalyptic number.

It is an amenable number.

81966565 is a deficient number, since it is larger than the sum of its proper divisors (16393319).

81966565 is a wasteful number, since it uses less digits than its factorization.

81966565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16393318.

The product of its digits is 388800, while the sum is 46.

The square root of 81966565 is about 9053.5388108739. The cubic root of 81966565 is about 434.3890926884.

The spelling of 81966565 in words is "eighty-one million, nine hundred sixty-six thousand, five hundred sixty-five".