20001809 has 8 divisors (see below), whose sum is σ = 21695688. Its totient is φ = 18365440.

The previous prime is 20001799. The next prime is 20001811. The reversal of 20001809 is 90810002.

It can be written as a sum of positive squares in 4 ways, for example, as 3025 + 19998784 = 55^2 + 4472^2 .

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

It is not a de Polignac number, because 20001809 - 2¹² = 19997713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20001899) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 13652 + ... + 15045.

It is an arithmetic number, because the mean of its divisors is an integer number (2711961).

Almost surely, 2^20001809 is an apocalyptic number.

It is an amenable number.

20001809 is a deficient number, since it is larger than the sum of its proper divisors (1693879).

20001809 is a wasteful number, since it uses less digits than its factorization.

20001809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 28755.

The product of its (nonzero) digits is 144, while the sum is 20.

The square root of 20001809 is about 4472.3382027749. The cubic root of 20001809 is about 271.4499453819.

The spelling of 20001809 in words is "twenty million, one thousand, eight hundred nine".