81965891 has 24 divisors (see below), whose sum is σ = 102798336. Its totient is φ = 63941760.

The previous prime is 81965887. The next prime is 81965893. The reversal of 81965891 is 19856918.

It is not a de Polignac number, because 81965891 - 2² = 81965887 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81965893) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 62060 + ... + 63366.

It is an arithmetic number, because the mean of its divisors is an integer number (4283264).

Almost surely, 2^81965891 is an apocalyptic number.

81965891 is a deficient number, since it is larger than the sum of its proper divisors (20832445).

81965891 is a wasteful number, since it uses less digits than its factorization.

81965891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1379 (or 1362 counting only the distinct ones).

The product of its digits is 155520, while the sum is 47.

The square root of 81965891 is about 9053.5015877836. The cubic root of 81965891 is about 434.3879020442.

The spelling of 81965891 in words is "eighty-one million, nine hundred sixty-five thousand, eight hundred ninety-one".