19999 has 4 divisors (see below), whose sum is σ = 22864. Its totient is φ = 17136.

The previous prime is 19997. The next prime is 20011. The reversal of 19999 is 99991.

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

It is not a de Polignac number, because 19999 - 2¹ = 19997 is a prime.

It is a fibodiv number, since the Fibonacci-like sequence with seeds 1 and 9999 contains 19999 itself.

It is a Duffinian number.

19999 is a modest number, since divided by 999 gives 19 as remainder.

It is a plaindrome in base 5 and base 10.

It is a zygodrome in base 5.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19991) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1422 + ... + 1435.

It is an arithmetic number, because the mean of its divisors is an integer number (5716).

2¹⁹⁹⁹⁹ is an apocalyptic number.

19999 is a deficient number, since it is larger than the sum of its proper divisors (2865).

19999 is an equidigital number, since it uses as much as digits as its factorization.

19999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2864.

The product of its digits is 6561, while the sum is 37.

The square root of 19999 is about 141.4178206592. The cubic root of 19999 is about 27.1437237555.

It can be divided in two parts, 199 and 99, that multiplied together give a triangular number (19701 = T₁₉₈).

The spelling of 19999 in words is "nineteen thousand, nine hundred ninety-nine".