81549865 has 4 divisors (see below), whose sum is σ = 97859844. Its totient is φ = 65239888.

The previous prime is 81549851. The next prime is 81549869. The reversal of 81549865 is 56894518.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 56894518 = 2 ⋅28447259.

It can be written as a sum of positive squares in 2 ways, for example, as 58201641 + 23348224 = 7629^2 + 4832^2 .

It is a cyclic number.

It is not a de Polignac number, because 81549865 - 2⁷ = 81549737 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81549869) 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 3 ways as a sum of consecutive naturals, for example, 8154982 + ... + 8154991.

It is an arithmetic number, because the mean of its divisors is an integer number (24464961).

Almost surely, 2^81549865 is an apocalyptic number.

It is an amenable number.

81549865 is a deficient number, since it is larger than the sum of its proper divisors (16309979).

81549865 is a wasteful number, since it uses less digits than its factorization.

81549865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16309978.

The product of its digits is 345600, while the sum is 46.

The square root of 81549865 is about 9030.4963872425. The cubic root of 81549865 is about 433.6517288522.

The spelling of 81549865 in words is "eighty-one million, five hundred forty-nine thousand, eight hundred sixty-five".