20646209 has 4 divisors (see below), whose sum is σ = 20655300. Its totient is φ = 20637120.

The previous prime is 20646187. The next prime is 20646221. The reversal of 20646209 is 90264602.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 15484225 + 5161984 = 3935^2 + 2272^2 .

It is a cyclic number.

It is not a de Polignac number, because 20646209 - 2¹⁶ = 20580673 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20646299) 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, 2117 + ... + 6765.

It is an arithmetic number, because the mean of its divisors is an integer number (5163825).

Almost surely, 2^20646209 is an apocalyptic number.

It is an amenable number.

20646209 is a deficient number, since it is larger than the sum of its proper divisors (9091).

20646209 is an equidigital number, since it uses as much as digits as its factorization.

20646209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9090.

The product of its (nonzero) digits is 5184, while the sum is 29.

The square root of 20646209 is about 4543.8099652164. The cubic root of 20646209 is about 274.3342972469.

The spelling of 20646209 in words is "twenty million, six hundred forty-six thousand, two hundred nine".