19905 has 8 divisors (see below), whose sum is σ = 31872. Its totient is φ = 10608.

The previous prime is 19891. The next prime is 19913. The reversal of 19905 is 50991.

It is a happy number.

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

It is not a de Polignac number, because 19905 - 2⁴ = 19889 is a prime.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 649 + ... + 678.

It is an arithmetic number, because the mean of its divisors is an integer number (3984).

2¹⁹⁹⁰⁵ is an apocalyptic number.

19905 is a gapful number since it is divisible by the number (15) formed by its first and last digit.

It is an amenable number.

19905 is a deficient number, since it is larger than the sum of its proper divisors (11967).

19905 is a wasteful number, since it uses less digits than its factorization.

19905 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1335.

The product of its (nonzero) digits is 405, while the sum is 24.

The square root of 19905 is about 141.0850807137. The cubic root of 19905 is about 27.1011296579.

Subtracting from 19905 its sum of digits (24), we obtain a square (19881 = 141²).

The spelling of 19905 in words is "nineteen thousand, nine hundred five".