20509209 has 12 divisors (see below), whose sum is σ = 33856576. Its totient is φ = 11719512.

The previous prime is 20509207. The next prime is 20509213. The reversal of 20509209 is 90290502.

It is not a de Polignac number, because 20509209 - 2¹ = 20509207 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20509207) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 162709 + ... + 162834.

Almost surely, 2^20509209 is an apocalyptic number.

It is an amenable number.

20509209 is a deficient number, since it is larger than the sum of its proper divisors (13347367).

20509209 is a wasteful number, since it uses less digits than its factorization.

20509209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 325556 (or 325553 counting only the distinct ones).

The product of its (nonzero) digits is 1620, while the sum is 27.

The square root of 20509209 is about 4528.7094188080. The cubic root of 20509209 is about 273.7261591798.

The spelling of 20509209 in words is "twenty million, five hundred nine thousand, two hundred nine".