20409 has 4 divisors (see below), whose sum is σ = 27216. Its totient is φ = 13604.

The previous prime is 20407. The next prime is 20411. The reversal of 20409 is 90402.

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 an interprime number because it is at equal distance from previous prime (20407) and next prime (20411).

It is a cyclic number.

It is not a de Polignac number, because 20409 - 2¹ = 20407 is a prime.

It is a D-number.

It is a Curzon number.

It is a plaindrome in base 7.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 20409.

It is not an unprimeable number, because it can be changed into a prime (20407) 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, 3399 + ... + 3404.

It is an arithmetic number, because the mean of its divisors is an integer number (6804).

2²⁰⁴⁰⁹ is an apocalyptic number.

It is an amenable number.

20409 is a deficient number, since it is larger than the sum of its proper divisors (6807).

20409 is an equidigital number, since it uses as much as digits as its factorization.

20409 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6806.

The product of its (nonzero) digits is 72, while the sum is 15.

The square root of 20409 is about 142.8600713986. The cubic root of 20409 is about 27.3279617973.

The spelling of 20409 in words is "twenty thousand, four hundred nine".