20309 has 4 divisors (see below), whose sum is σ = 21216. Its totient is φ = 19404.

The previous prime is 20297. The next prime is 20323. The reversal of 20309 is 90302.

20309 = T₃₀ + T₃₁ + ... + T₅₂.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20309 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20293 and 20302.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20359) 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, 419 + ... + 464.

It is an arithmetic number, because the mean of its divisors is an integer number (5304).

2²⁰³⁰⁹ is an apocalyptic number.

It is an amenable number.

20309 is a deficient number, since it is larger than the sum of its proper divisors (907).

20309 is an equidigital number, since it uses as much as digits as its factorization.

20309 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 906.

The product of its (nonzero) digits is 54, while the sum is 14.

The square root of 20309 is about 142.5096487961. The cubic root of 20309 is about 27.2832548583.

The spelling of 20309 in words is "twenty thousand, three hundred nine".