20778209 has 4 divisors (see below), whose sum is σ = 21062916. Its totient is φ = 20493504.

The previous prime is 20778203. The next prime is 20778211. The reversal of 20778209 is 90287702.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 12780625 + 7997584 = 3575^2 + 2828^2 .

It is a cyclic number.

It is not a de Polignac number, because 20778209 - 2²⁴ = 4000993 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (20778203) 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, 142244 + ... + 142389.

It is an arithmetic number, because the mean of its divisors is an integer number (5265729).

Almost surely, 2^20778209 is an apocalyptic number.

It is an amenable number.

20778209 is a deficient number, since it is larger than the sum of its proper divisors (284707).

20778209 is an equidigital number, since it uses as much as digits as its factorization.

20778209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 284706.

The product of its (nonzero) digits is 14112, while the sum is 35.

The square root of 20778209 is about 4558.3120779517. The cubic root of 20778209 is about 274.9177009927.

The spelling of 20778209 in words is "twenty million, seven hundred seventy-eight thousand, two hundred nine".