81511 has 4 divisors (see below), whose sum is σ = 83752. Its totient is φ = 79272.

The previous prime is 81509. The next prime is 81517. The reversal of 81511 is 11518.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81511 - 2¹ = 81509 is a prime.

It is the 286-th Hogben number.

It is a Duffinian number.

81511 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81517) by changing a digit.

It is a nontrivial repunit in base 285.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1065 + ... + 1138.

It is an arithmetic number, because the mean of its divisors is an integer number (20938).

2⁸¹⁵¹¹ is an apocalyptic number.

81511 is a deficient number, since it is larger than the sum of its proper divisors (2241).

81511 is a wasteful number, since it uses less digits than its factorization.

81511 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2240.

The product of its digits is 40, while the sum is 16.

The square root of 81511 is about 285.5013134821. The cubic root of 81511 is about 43.3582828053.

The spelling of 81511 in words is "eighty-one thousand, five hundred eleven".