81945 has 16 divisors (see below), whose sum is σ = 145920. Its totient is φ = 43632.

The previous prime is 81943. The next prime is 81953. The reversal of 81945 is 54918.

It is not a de Polignac number, because 81945 - 2¹ = 81943 is a prime.

It is a Smith number, since the sum of its digits (27) coincides with the sum of the digits of its prime factors.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (81943) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 169 + ... + 438.

It is an arithmetic number, because the mean of its divisors is an integer number (9120).

2⁸¹⁹⁴⁵ is an apocalyptic number.

It is an amenable number.

81945 is a deficient number, since it is larger than the sum of its proper divisors (63975).

81945 is a wasteful number, since it uses less digits than its factorization.

81945 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 621 (or 615 counting only the distinct ones).

The product of its digits is 1440, while the sum is 27.

The square root of 81945 is about 286.2603709912. The cubic root of 81945 is about 43.4350994136.

Subtracting from 81945 its sum of digits (27), we obtain a palindrome (81918).

It can be divided in two parts, 8 and 1945, that added together give a triangular number (1953 = T₆₂).

The spelling of 81945 in words is "eighty-one thousand, nine hundred forty-five".