81005 has 8 divisors (see below), whose sum is σ = 103032. Its totient is φ = 60928.

The previous prime is 81001. The next prime is 81013. The reversal of 81005 is 50018.

81005 = T₈₉ + T₉₀ + ... + T₁₀₅.

It can be written as a sum of positive squares in 4 ways, for example, as 13924 + 67081 = 118^2 + 259^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 81005 - 2² = 81001 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81001) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 392 + ... + 561.

It is an arithmetic number, because the mean of its divisors is an integer number (12879).

2⁸¹⁰⁰⁵ is an apocalyptic number.

81005 is a gapful number since it is divisible by the number (85) formed by its first and last digit.

It is an amenable number.

81005 is a deficient number, since it is larger than the sum of its proper divisors (22027).

81005 is a wasteful number, since it uses less digits than its factorization.

81005 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 975.

The product of its (nonzero) digits is 40, while the sum is 14.

The square root of 81005 is about 284.6137733842. The cubic root of 81005 is about 43.2683773684.

The spelling of 81005 in words is "eighty-one thousand, five".