20431209 has 4 divisors (see below), whose sum is σ = 27241616. Its totient is φ = 13620804.

The previous prime is 20431171. The next prime is 20431211. The reversal of 20431209 is 90213402.

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 de Polignac number, because none of the positive numbers 2^k-20431209 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20431219) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3405199 + ... + 3405204.

It is an arithmetic number, because the mean of its divisors is an integer number (6810404).

Almost surely, 2^20431209 is an apocalyptic number.

It is an amenable number.

20431209 is a deficient number, since it is larger than the sum of its proper divisors (6810407).

20431209 is an equidigital number, since it uses as much as digits as its factorization.

20431209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6810406.

The product of its (nonzero) digits is 432, while the sum is 21.

The square root of 20431209 is about 4520.0894902645. The cubic root of 20431209 is about 273.3787093350.

It can be divided in two parts, 204 and 31209, that multiplied together give a palindrome (6366636).

The spelling of 20431209 in words is "twenty million, four hundred thirty-one thousand, two hundred nine".