19809 has 12 divisors (see below), whose sum is σ = 29952. Its totient is φ = 12600.

The previous prime is 19801. The next prime is 19813. The reversal of 19809 is 90891.

It is not a de Polignac number, because 19809 - 2³ = 19801 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19801) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 244 + ... + 314.

It is an arithmetic number, because the mean of its divisors is an integer number (2496).

2¹⁹⁸⁰⁹ is an apocalyptic number.

It is an amenable number.

19809 is a deficient number, since it is larger than the sum of its proper divisors (10143).

19809 is a wasteful number, since it uses less digits than its factorization.

19809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 108 (or 105 counting only the distinct ones).

The product of its (nonzero) digits is 648, while the sum is 27.

The square root of 19809 is about 140.7444492689. The cubic root of 19809 is about 27.0574906679.

It can be divided in two parts, 19 and 809, that added together give a palindrome (828).

The spelling of 19809 in words is "nineteen thousand, eight hundred nine".