15805 has 8 divisors (see below), whose sum is σ = 19800. Its totient is φ = 12096.

The previous prime is 15803. The next prime is 15809. The reversal of 15805 is 50851.

15805 = T₇₇ + T₇₈ + ... + T₈₁.

It can be written as a sum of positive squares in 4 ways, for example, as 2809 + 12996 = 53^2 + 114^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 15805 - 2¹ = 15803 is a prime.

15805 is an undulating number in base 12.

15805 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (15803) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 91 + ... + 199.

It is an arithmetic number, because the mean of its divisors is an integer number (2475).

2¹⁵⁸⁰⁵ is an apocalyptic number.

It is an amenable number.

15805 is a deficient number, since it is larger than the sum of its proper divisors (3995).

15805 is a wasteful number, since it uses less digits than its factorization.

15805 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 143.

The product of its (nonzero) digits is 200, while the sum is 19.

The square root of 15805 is about 125.7179382586. The cubic root of 15805 is about 25.0956337013.

It can be divided in two parts, 15 and 805, that added together give a triangular number (820 = T₄₀).

The spelling of 15805 in words is "fifteen thousand, eight hundred five".