81641865 has 16 divisors (see below), whose sum is σ = 133814016. Its totient is φ = 42480000.

The previous prime is 81641849. The next prime is 81641887. The reversal of 81641865 is 56814618.

It is not a de Polignac number, because 81641865 - 2⁴ = 81641849 is a prime.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 65761 + ... + 66990.

It is an arithmetic number, because the mean of its divisors is an integer number (8363376).

Almost surely, 2^81641865 is an apocalyptic number.

It is an amenable number.

81641865 is a deficient number, since it is larger than the sum of its proper divisors (52172151).

81641865 is a wasteful number, since it uses less digits than its factorization.

81641865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 132800.

The product of its digits is 46080, while the sum is 39.

The square root of 81641865 is about 9035.5888020649. The cubic root of 81641865 is about 433.8147414484.

The spelling of 81641865 in words is "eighty-one million, six hundred forty-one thousand, eight hundred sixty-five".