19865 has 8 divisors (see below), whose sum is σ = 24840. Its totient is φ = 15232.

The previous prime is 19861. The next prime is 19867. The reversal of 19865 is 56891.

It can be written as a sum of positive squares in 4 ways, for example, as 2704 + 17161 = 52^2 + 131^2 .

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 19865 - 2² = 19861 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (29).

19865 is an undulating number in base 12.

It is not an unprimeable number, because it can be changed into a prime (19861) 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, 77 + ... + 213.

It is an arithmetic number, because the mean of its divisors is an integer number (3105).

2¹⁹⁸⁶⁵ is an apocalyptic number.

It is an amenable number.

19865 is a deficient number, since it is larger than the sum of its proper divisors (4975).

19865 is a wasteful number, since it uses less digits than its factorization.

19865 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 171.

The product of its digits is 2160, while the sum is 29.

The square root of 19865 is about 140.9432509913. The cubic root of 19865 is about 27.0829638345.

It can be divided in two parts, 1986 and 5, that added together give a palindrome (1991).

The spelling of 19865 in words is "nineteen thousand, eight hundred sixty-five".