199809 has 9 divisors (see below), whose sum is σ = 290563.
Its totient is φ = 132312.
The previous prime is 199807. The next prime is 199811. The reversal of 199809 is 908991.
199809 = T446 + T447.
The square root of 199809 is 447.
It is a perfect power (a square), and thus also a powerful number.
It is an interprime number because it is at equal distance from previous prime (199807) and next prime (199811).
It can be written as a sum of positive squares in only one way, i.e., 23409 + 176400 = 153^2 + 420^2
It is a tau number, because it is divible by the number of its divisors (9).
It is not a de Polignac number, because 199809 - 21 = 199807 is a prime.
It is a Duffinian number.
It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 199809.
It is not an unprimeable number, because it can be changed into a prime (199807) by changing a digit.
It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 1267 + ... + 1415.
2199809 is an apocalyptic number.
199809 is the 447-th square number.
199809 is the 224-th centered octagonal number.
It is an amenable number.
199809 is a deficient number, since it is larger than the sum of its proper divisors (90754).
199809 is an equidigital number, since it uses as much as digits as its factorization.
199809 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 304 (or 152 counting only the distinct ones).
The product of its (nonzero) digits is 5832, while the sum is 36.
The cubic root of 199809 is about 58.4617325887.
Multiplying 199809 by its sum of digits (36), we get a square (7193124 = 26822).
The spelling of 199809 in words is "one hundred ninety-nine thousand, eight hundred nine".